stringobject.py

import copy
import string
import math

from rpython.rlib import jit
from rpython.rlib.objectmodel import newlist_hint, compute_hash
from rpython.rlib.rarithmetic import intmask, ovfcheck
from rpython.rlib.rbigint import rbigint
from rpython.rlib.rerased import new_static_erasing_pair
from rpython.rlib.rsre import rsre_core
from rpython.rlib.rstring import split

from topaz.module import ClassDef, check_frozen
from topaz.modules.comparable import Comparable
from topaz.objects.objectobject import W_Object
from topaz.utils.formatting import StringFormatter


def create_trans_table(source, replacement, inv=False):
    src = expand_trans_str(source, len(source), inv)
    repl = expand_trans_str(replacement, len(src))
    table = [chr(i) for i in xrange(256)]
    for i, c in enumerate(src):
        table[ord(c)] = repl[i]
    return table


def expand_trans_str(source, res_len, inv=False):
    # check the source for range definitions
    # and insert the missing characters
    expanded_source = []
    char = ""
    for i in range(res_len):
        if i < len(source):
            char = source[i]
        if char == "-":
            # expand the range
            assert 0 < i < len(source) - 1
            range_beg = ord(source[i - 1])
            range_end = ord(source[i + 1])
            for j in range(range_beg + 1, range_end - 1):
                expanded_source.append(chr(j))
        elif char:
            expanded_source.append(char[0])

    if inv:
        inverted_source = []
        # invert the source
        for i in range(256):
            if chr(i) not in expanded_source:
                inverted_source.append(chr(i))
        return inverted_source

    return expanded_source


class StringStrategy(object):
    def __init__(self, space):
        pass

    def __deepcopy__(self, memo):
        memo[id(self)] = result = object.__new__(self.__class__)
        return result


class ConstantStringStrategy(StringStrategy):
    erase, unerase = new_static_erasing_pair("constant")

    def str_w(self, storage):
        return self.unerase(storage)

    def liststr_w(self, storage):
        strvalue = self.unerase(storage)
        return [c for c in strvalue]

    def length(self, storage):
        return len(self.unerase(storage))

    def getitem(self, storage, idx):
        return self.unerase(storage)[idx]

    def getslice(self, space, storage, start, end):
        return space.newstr_fromstr(self.unerase(storage)[start:end])

    def hash(self, storage):
        return compute_hash(self.unerase(storage))

    def copy(self, storage):
        return storage

    def to_mutable(self, space, s):
        s.strategy = strategy = space.fromcache(MutableStringStrategy)
        s.str_storage = strategy.erase(self.liststr_w(s.str_storage))

    def extend_into(self, src_storage, dst_storage):
        dst_storage += self.unerase(src_storage)

    def mul(self, space, storage, times):
        return space.newstr_fromstr(self.unerase(storage) * times)


class MutableStringStrategy(StringStrategy):
    erase, unerase = new_static_erasing_pair("mutable")

    def str_w(self, storage):
        return "".join(self.unerase(storage))

    def liststr_w(self, storage):
        return self.unerase(storage)

    def length(self, storage):
        return len(self.unerase(storage))

    def getitem(self, storage, idx):
        return self.unerase(storage)[idx]

    def getslice(self, space, storage, start, end):
        return space.newstr_fromchars(self.unerase(storage)[start:end])

    def hash(self, storage):
        storage = self.unerase(storage)
        length = len(storage)
        if length == 0:
            return -1
        x = ord(storage[0]) << 7
        i = 0
        while i < length:
            x = intmask((1000003 * x) ^ ord(storage[i]))
            i += 1
        x ^= length
        return intmask(x)

    def copy(self, storage):
        return self.erase(self.unerase(storage)[:])

    def to_mutable(self, space, s):
        pass

    def extend_into(self, src_storage, dst_storage):
        dst_storage += self.unerase(src_storage)

    def clear(self, s):
        storage = self.unerase(s.str_storage)
        del storage[:]

    def mul(self, space, storage, times):
        return space.newstr_fromchars(self.unerase(storage) * times)

    def reverse(self, storage):
        storage = self.unerase(storage)
        storage.reverse()

    def swapcase(self, storage):
        storage = self.unerase(storage)
        changed = False
        for i, c in enumerate(storage):
            if ord("A") <= ord(c) <= ord("Z"):
                new_c = c.lower()
                changed = True
            elif ord("a") <= ord(c) <= ord("z"):
                new_c = c.upper()
                changed = True
            else:
                new_c = c
            storage[i] = new_c
        return changed

    def downcase(self, storage):
        storage = self.unerase(storage)
        changed = False
        for i, c in enumerate(storage):
            new_c = c.lower()
            changed |= (c != new_c)
            storage[i] = new_c
        return changed

    def upcase(self, storage):
        storage = self.unerase(storage)
        changed = False
        for i, c in enumerate(storage):
            new_c = c.upper()
            changed |= (c != new_c)
            storage[i] = new_c
        return changed

    def capitalize(self, storage):
        storage = self.unerase(storage)
        changed = False
        for i, c in enumerate(storage):
            if i == 0:
                new_c = c.upper()
            else:
                new_c = c.lower()
            changed |= (c != new_c)
            storage[i] = new_c
        return changed

    def chomp(self, storage, newline=None):
        storage = self.unerase(storage)
        changed = False
        if len(storage) == 0:
            return changed
        elif newline is not None and len(storage) >= len(newline):
            for i in xrange(len(newline) - 1, -1, -1):
                if newline[i] != storage[len(storage) - len(newline) + i]:
                    return changed
            start = len(storage) - len(newline)
            assert start >= 0
            del storage[start:]
            changed = True
        elif newline is None:
            ch = storage[-1]
            i = len(storage) - 1
            while i >= 0 and ch in "\n\r":
                i -= 1
                ch = storage[i]
            if i < len(storage) - 1:
                i += 1
                changed = True
                if i > 0:
                    del storage[i:]
                else:
                    del storage[:]
        return changed

    def chop(self, storage):
        storage = self.unerase(storage)
        if len(storage) == 0:
            return False
        elif storage[-1] == "\n" and len(storage) >= 2 and storage[-2] == "\r":
            idx = len(storage) - 2
            assert idx >= 0
            del storage[idx:]
            return True
        else:
            del storage[-1]
            return True

    def succ(self, storage):
        storage = self.unerase(storage)
        if len(storage) == 0:
            return

        carry = "\0"
        has_alnums = False
        last_alnum = 0
        start = len(storage) - 1

        while start >= 0:
            ch = storage[start]
            if ch in string.letters or ch in string.digits:
                has_alnums = True
                if ch == "9":
                    carry = "1"
                    storage[start] = "0"
                elif ch == "z":
                    carry = "a"
                    storage[start] = "a"
                elif ch == "Z":
                    carry = "A"
                    storage[start] = "A"
                else:
                    storage[start] = chr(ord(ch) + 1)
                    carry = "\0"

                if carry == "\0":
                    break
                last_alnum = start
            start -= 1

        if not has_alnums:
            start = len(storage) - 1
            carry = "\1"

            while start >= 0:
                ch = storage[start]
                if ord(ch) >= 255:
                    storage[start] = "\0"
                else:
                    storage[start] = chr(ord(ch) + 1)
                    break
                start -= 1

        if start < 0 and carry != "\0":
            last_alnum_ch = storage[last_alnum]
            storage[last_alnum] = carry
            storage.insert(last_alnum + 1, last_alnum_ch)

    def insert(self, storage, idx, other):
        storage = self.unerase(storage)
        for char in other:
            storage.insert(idx, char)
            idx += 1


class W_StringObject(W_Object):
    classdef = ClassDef("String", W_Object.classdef, filepath=__file__)
    classdef.include_module(Comparable)

    def __init__(self, space, storage, strategy):
        W_Object.__init__(self, space)
        self.str_storage = storage
        self.strategy = strategy

    def __deepcopy__(self, memo):
        obj = super(W_StringObject, self).__deepcopy__(memo)
        obj.str_storage = copy.deepcopy(self.str_storage, memo)
        obj.strategy = copy.deepcopy(self.strategy, memo)
        return obj

    @staticmethod
    def newstr_fromstr(space, strvalue):
        strategy = space.fromcache(ConstantStringStrategy)
        storage = strategy.erase(strvalue)
        return W_StringObject(space, storage, strategy)

    @staticmethod
    @jit.look_inside_iff(lambda space, strs_w: jit.isconstant(len(strs_w)))
    def newstr_fromstrs(space, strs_w):
        total_length = 0
        for w_item in strs_w:
            assert isinstance(w_item, W_StringObject)
            total_length += w_item.length()

        storage = newlist_hint(total_length)
        for w_item in strs_w:
            assert isinstance(w_item, W_StringObject)
            w_item.strategy.extend_into(w_item.str_storage, storage)
        return space.newstr_fromchars(storage)

    @staticmethod
    def newstr_fromchars(space, chars):
        strategy = space.fromcache(MutableStringStrategy)
        storage = strategy.erase(chars)
        return W_StringObject(space, storage, strategy)

    def str_w(self, space):
        return self.strategy.str_w(self.str_storage)

    def liststr_w(self, space):
        return self.strategy.liststr_w(self.str_storage)

    def length(self):
        return self.strategy.length(self.str_storage)

    def copy(self, space):
        return W_StringObject(space, self.strategy.copy(self.str_storage), self.strategy)

    def replace(self, space, chars):
        strategy = space.fromcache(MutableStringStrategy)
        self.str_storage = strategy.erase(chars)
        self.strategy = strategy

    def extend(self, space, w_other):
        self.strategy.to_mutable(space, self)
        strategy = self.strategy
        assert isinstance(strategy, MutableStringStrategy)
        storage = strategy.unerase(self.str_storage)
        w_other.strategy.extend_into(w_other.str_storage, storage)

    def clear(self, space):
        self.strategy.to_mutable(space, self)
        self.strategy.clear(self)

    def tr_trans(self, space, source, replacement, squeeze):
        change_made = False
        string = space.str_w(self)
        new_string = []
        is_negative_set = len(source) > 1 and source[0] == "^"
        if is_negative_set:
            source = source[1:]

        trans_table = create_trans_table(source, replacement, is_negative_set)

        if squeeze:
            last_repl = ""
            for char in string:
                repl = trans_table[ord(char)]
                if last_repl == repl:
                    continue
                if repl != char:
                    last_repl = repl
                    if not change_made:
                        change_made = True
                new_string.append(repl)
        else:
            for char in string:
                repl = trans_table[ord(char)]
                if not change_made and repl != char:
                    change_made = True
                new_string.append(repl)

        return new_string if change_made else None

    @classdef.singleton_method("allocate")
    def singleton_method_allocate(self, space, w_s=None):
        return space.newstr_fromstr("")

    @classdef.method("initialize")
    def method_initialize(self, space, w_s=None):
        if w_s is not None:
            w_s = space.convert_type(w_s, space.w_string, "to_str")
            assert isinstance(w_s, W_StringObject)
            self.strategy = w_s.strategy
            self.str_storage = w_s.strategy.copy(w_s.str_storage)

    @classdef.method("initialize_copy")
    def method_initialize_copy(self, space, w_other):
        assert isinstance(w_other, W_StringObject)
        self.strategy = w_other.strategy
        self.str_storage = w_other.strategy.copy(w_other.str_storage)
        return self

    @classdef.method("to_str")
    @classdef.method("to_s")
    def method_to_s(self, space):
        return self

    @classdef.method("ord")
    def method_ord(self, space):
        if self.length() == 0:
            raise space.error(space.w_ArgumentError, "empty string")
        return space.newint(ord(self.strategy.getitem(self.str_storage, 0)))

    @classdef.method("inspect")
    def method_inspect(self, space):
        return space.newstr_fromstr('"%s"' % self.str_w(space))

    @classdef.method("+")
    def method_plus(self, space, w_obj):
        if space.is_kind_of(w_obj, space.w_string):
            w_other = w_obj
        else:
            w_other = space.convert_type(w_obj, space.w_string, "to_str")
        assert isinstance(w_other, W_StringObject)
        total_size = self.length() + w_other.length()
        s = space.newstr_fromchars(newlist_hint(total_size))
        s.extend(space, self)
        s.extend(space, w_other)
        return s

    @classdef.method("*", times="int")
    def method_times(self, space, times):
        return self.strategy.mul(space, self.str_storage, times)

    @classdef.method("<<")
    def method_lshift(self, space, w_other):
        assert isinstance(w_other, W_StringObject)
        self.extend(space, w_other)
        return self

    @classdef.method("size")
    @classdef.method("length")
    def method_length(self, space):
        return space.newint(self.length())

    @classdef.method("hash")
    def method_hash(self, space):
        return space.newint(self.strategy.hash(self.str_storage))

    @classdef.method("[]")
    def method_subscript(self, space, w_idx, w_count=None):
        start, end, as_range, nil = space.subscript_access(self.length(), w_idx, w_count=w_count)
        if nil:
            return space.w_nil
        elif as_range:
            assert start >= 0
            assert end >= 0
            return self.strategy.getslice(space, self.str_storage, start, end)
        else:
            return space.newstr_fromstr(self.strategy.getitem(self.str_storage, start))

    @classdef.method("<=>")
    def method_comparator(self, space, w_other):
        if isinstance(w_other, W_StringObject):
            s1 = space.str_w(self)
            s2 = space.str_w(w_other)
            if s1 < s2:
                return space.newint(-1)
            elif s1 == s2:
                return space.newint(0)
            elif s1 > s2:
                return space.newint(1)
        else:
            if space.respond_to(w_other, space.newsymbol("to_str")) and space.respond_to(w_other, space.newsymbol("<=>")):
                tmp = space.send(w_other, space.newsymbol("<=>"), [self])
                if tmp is not space.w_nil:
                    return space.newint(-space.int_w(tmp))
            return space.w_nil

    @classdef.method("to_sym")
    @classdef.method("intern")
    def method_to_sym(self, space):
        return space.newsymbol(space.str_w(self))

    @classdef.method("clear")
    def method_clear(self, space):
        self.clear(space)
        return self

    @classdef.method("ljust", integer="int", padstr="str")
    def method_ljust(self, space, integer, padstr=" "):
        if not padstr:
            raise space.error(space.w_ArgumentError, "zero width padding")
        elif integer <= self.length():
            return self.copy(space)
        else:
            pad_len = integer - self.length() - 1
            assert pad_len >= 0
            chars = []
            chars += space.str_w(self)
            for i in xrange(pad_len / len(padstr)):
                chars += padstr
            chars += padstr[:pad_len % len(padstr) + 1]
            return space.newstr_fromchars(chars)

    def search_context(self, space, ctx):
        try:
            return rsre_core.search_context(ctx)
        except rsre_core.Error, e:
            raise space.error(space.w_RuntimeError, e.msg)

    @classdef.method("index", offset="int")
    def method_index(self, space, w_sub, offset=0):
        if offset < 0 or offset >= self.length():
            return space.w_nil
        elif space.is_kind_of(w_sub, space.w_string):
            return space.newint(space.str_w(self).find(space.str_w(w_sub), offset))
        elif space.is_kind_of(w_sub, space.w_regexp):
            ctx = w_sub.make_ctx(space.str_w(self), offset=offset)
            if self.search_context(space, ctx):
                return space.newint(ctx.match_start)
            else:
                return space.newint(-1)
        else:
            raise space.error(
                space.w_TypeError,
                "type mismatch: %s given" %
                    space.obj_to_s(space.getclass(w_sub))
            )

    @classdef.method("rindex", end="int")
    def method_rindex(self, space, w_sub, end=0):
        if end < 0:
            end += self.length()
        else:
            end = self.length()
        if end < 0:
            return space.w_nil

        idx = -1
        if space.is_kind_of(w_sub, space.w_string):
            idx = space.str_w(self).rfind(space.str_w(w_sub), 0, end + 1)
        elif space.is_kind_of(w_sub, space.w_regexp):
            ctx = w_sub.make_ctx(space.str_w(self))
            idx = -1
            while self.search_context(space, ctx):
                if ctx.match_start > end:
                    break
                else:
                    idx = ctx.match_start
                ctx.reset(idx + 1)
        else:
            raise space.error(
                space.w_TypeError,
                "type mismatch: %s given" %
                    space.obj_to_s(space.getclass(w_sub))
            )
        if idx < 0:
            return space.w_nil
        else:
            return space.newint(idx)

    @classdef.method("split", limit="int")
    def method_split(self, space, w_sep=None, limit=0):
        if w_sep is None:
            res_w = []
            i = 0
            limit -= 1
            s = space.str_w(self)
            while True:
                while i < len(s):
                    if not s[i].isspace():
                        break
                    i += 1
                else:
                    break
                if limit == 0:
                    j = len(s)
                else:
                    j = i + 1
                    while j < len(s) and not s[j].isspace():
                        j += 1
                    limit -= 1
                res_w.append(space.newstr_fromstr(s[i:j]))
                i = j + 1
            return space.newarray(res_w)
        elif space.is_kind_of(w_sep, space.w_string):
            sep = space.str_w(w_sep)
            return space.newarray([
                space.newstr_fromstr(s) for s in split(space.str_w(self), sep, limit - 1)
            ])
        elif space.is_kind_of(w_sep, space.w_regexp):
            results_w = []
            n = 0
            last = 0
            string = space.str_w(self)
            ctx = w_sep.make_ctx(string)
            w_match = w_sep.get_match_result(space, ctx, found=True)

            while limit <= 0 or n + 1 < limit:
                if not self.search_context(space, ctx):
                    break
                elif ctx.match_start == ctx.match_end:
                    if ctx.match_start == ctx.end:
                        break
                    results_w.append(space.newstr_fromstr(string[last]))
                    last = ctx.match_end + 1
                else:
                    results_w.append(space.newstr_fromstr(string[last:ctx.match_start]))
                    for num in xrange(1, w_match.size(), 1):
                        begin, end = w_match.get_span(num)
                        begin += last
                        end += last
                        assert begin >= 0
                        assert end >= 0
                        results_w.append(space.newstr_fromstr(string[begin:end]))
                    last = ctx.match_end
                n += 1
                ctx.reset(last)

            if len(string) > last:
                results_w.append(space.newstr_fromstr(string[last:]))
            if limit < 0 or len(results_w) < limit:
                results_w.append(space.newstr_fromstr(""))
            return space.newarray(results_w)

        else:
            raise space.error(
                space.w_TypeError,
                "wrong argument type %s (expected Regexp)" %
                    space.obj_to_s(space.getclass(w_sep))
            )

    @classdef.method("swapcase!")
    def method_swapcase_i(self, space):
        self.strategy.to_mutable(space, self)
        changed = self.strategy.swapcase(self.str_storage)
        return self if changed else space.w_nil

    @classdef.method("upcase!")
    def method_upcase_i(self, space):
        self.strategy.to_mutable(space, self)
        changed = self.strategy.upcase(self.str_storage)
        return self if changed else space.w_nil

    @classdef.method("downcase!")
    def method_downcase_i(self, space):
        self.strategy.to_mutable(space, self)
        changed = self.strategy.downcase(self.str_storage)
        return self if changed else space.w_nil

    @classdef.method("capitalize!")
    def method_capitalize_i(self, space):
        self.strategy.to_mutable(space, self)
        changed = self.strategy.capitalize(self.str_storage)
        return self if changed else space.w_nil

    def _digits(self, s, i, radix):
        number_seen = False
        while i < len(s):
            c = ord(s[i])
            if c == ord("_") and number_seen:
                i += 1
                continue
            if ord("a") <= c <= ord("z"):
                digit = c - ord("a") + 10
            elif ord("A") <= c <= ord("Z"):
                digit = c - ord("A") + 10
            elif ord("0") <= c <= ord("9"):
                digit = c - ord("0")
            else:
                break
            if digit >= radix:
                break
            number_seen = True
            yield digit
            i += 1

    def to_int(self, s, neg, i, radix):
        val = 0
        for digit in self._digits(s, i, radix):
            val = ovfcheck(val * radix + digit)
        if neg:
            val = -val
        return val

    def to_bigint(self, s, neg, i, radix):
        val = rbigint.fromint(0)
        bigint_radix = rbigint.fromint(radix)
        for digit in self._digits(s, i, radix):
            val = val.mul(bigint_radix).add(rbigint.fromint(digit))
        if neg:
            val = val.neg()
        return val

    @classdef.method("to_i", radix="int")
    def method_to_i(self, space, radix=10):
        if not 2 <= radix <= 36:
            raise space.error(space.w_ArgumentError, "invalid radix %d" % radix)
        s = space.str_w(self)
        i = 0
        while i < len(s):
            if not s[i].isspace():
                break
            i += 1
        neg = i < len(s) and s[i] == "-"
        if neg:
            i += 1
        try:
            value = self.to_int(s, neg, i, radix)
        except OverflowError:
            value = self.to_bigint(s, neg, i, radix)
            return space.newbigint_fromrbigint(value)
        else:
            return space.newint(value)

    @classdef.method("to_f")
    def method_to_f(self, space):
        value = 0.0
        precision = False
        pointer = 0.1
        negative = False
        exponent = False
        multi = 0
        number = False

        for char in space.str_w(self):
            c = ord(char)
            if ord("0") <= c <= ord("9"):
                if exponent:
                    multi = multi * 10 + c - ord("0")
                elif precision:
                    value = value + pointer * (c - ord("0"))
                    pointer /= 10
                else:
                    value = value * 10 + c - ord("0")

                number = True
            elif c == ord("-"):
                if value != 0.0:
                    break
                negative = not negative
            elif c == ord("+"):
                if value != 0.0:
                    break
                pass
            elif c == ord("."):
                if precision or exponent:
                    break
                precision = True
            elif c == ord("e"):
                if exponent:
                    break
                exponent = True
            elif char.isspace():
                if number:
                    break
            else:
                break

        if exponent:
            value = value * math.pow(10, multi)

        return space.newfloat(value)

    @classdef.method("tr", source="str", replacement="str")
    def method_tr(self, space, source, replacement):
        string = self.copy(space)
        new_string = self.tr_trans(space, source, replacement, False)
        return space.newstr_fromchars(new_string) if new_string else string

    @classdef.method("tr!", source="str", replacement="str")
    def method_tr_i(self, space, source, replacement):
        new_string = self.tr_trans(space, source, replacement, False)
        self.replace(space, new_string)
        return self if new_string else space.w_nil

    @classdef.method("tr_s", source="str", replacement="str")
    def method_tr_s(self, space, source, replacement):
        string = self.copy(space)
        new_string = self.tr_trans(space, source, replacement, True)
        return space.newstr_fromchars(new_string) if new_string else string

    @classdef.method("tr_s!", source="str", replacement="str")
    def method_tr_s_i(self, space, source, replacement):
        new_string = self.tr_trans(space, source, replacement, True)
        self.replace(space, new_string)
        return self if new_string else space.w_nil

    @classdef.method("=~")
    def method_match_operator(self, space, w_obj):
        if space.is_kind_of(w_obj, space.w_string):
            raise space.error(space.w_TypeError, "type mismatch: String given")
        else:
            return space.send(w_obj, space.newsymbol("=~"), [self])

    @classdef.method("%")
    def method_mod(self, space, w_arg):
        if space.is_kind_of(w_arg, space.w_array):
            args_w = space.listview(w_arg)
        else:
            args_w = [w_arg]
        elements_w = StringFormatter(space.str_w(self), args_w).format(space)
        return space.newstr_fromstrs(elements_w)

    @classdef.method("getbyte", pos="int")
    def method_getbyte(self, space, pos):
        if pos >= self.length() or pos < -self.length():
            return space.w_nil
        if pos < 0:
            pos += self.length()
        ch = self.strategy.getitem(self.str_storage, pos)
        return space.newint(ord(ch))

    @classdef.method("include?", substr="str")
    def method_includep(self, space, substr):
        return space.newbool(substr in space.str_w(self))

    @classdef.method("gsub")
    def method_gsub(self, space, w_pattern, w_replacement=None, block=None):
        return self.gsub_main(space, w_pattern, w_replacement, block, first_only=False)

    @classdef.method("sub")
    def method_sub(self, space, w_pattern, w_replacement=None, block=None):
        return self.gsub_main(space, w_pattern, w_replacement, block, first_only=True)

    def gsub_main(self, space, w_pattern, w_replacement, block, first_only):
        if w_replacement is None and block is None:
            raise NotImplementedError("gsub enumerator")

        w_hash = None
        replacement = None
        if w_replacement:
            w_hash = space.convert_type(w_replacement, space.w_hash, "to_hash", raise_error=False)
            if w_hash is space.w_nil:
                w_hash = None
                replacement = space.str_w(
                    space.convert_type(w_replacement, space.w_string, "to_str")
                )

        if space.is_kind_of(w_pattern, space.w_regexp):
            return self.gsub_regexp(space, w_pattern, replacement, w_hash, block, first_only)
        elif space.is_kind_of(w_pattern, space.w_string):
            return self.gsub_string(space, w_pattern, replacement, w_hash, block, first_only)
        else:
            raise space.error(
                space.w_TypeError,
                "wrong argument type %s (expected Regexp)" %
                    space.obj_to_s(space.getclass(w_replacement))
            )

    def gsub_regexp(self, space, w_pattern, replacement, w_hash, block, first_only):
        result = []
        pos = 0
        string = space.str_w(self)
        ctx = w_pattern.make_ctx(string)

        w_matchdata = w_pattern.get_match_result(space, ctx, found=True)
        replacement_parts = None
        if replacement is not None and "\\" in replacement:
            replacement_parts = [s for s in replacement.split("\\") if s]

        while pos < len(string) and self.search_context(space, ctx):
            result += string[pos:ctx.match_start]
            if replacement_parts is not None:
                result += (self.gsub_regexp_subst_string(
                        space, replacement_parts, w_matchdata, pos
                ))
            elif replacement is not None:
                result += replacement
            elif block:
                result += self.gsub_regexp_block(space, block, w_matchdata)
            elif w_hash:
                result += self.gsub_regexp_hash(space, w_hash, w_matchdata)
            pos = ctx.match_end
            ctx.reset(pos)
            if first_only:
                break
        result += string[pos:]
        return space.newstr_fromchars(result)

    def gsub_regexp_subst_string(self, space, parts_w, w_match, pos=0):
        result = []
        string = space.str_w(self)
        result += parts_w[0]
        for s in parts_w[1:]:
            if s[0].isdigit():
                group = int(s[0])
                if group < w_match.size():
                    begin, end = w_match.get_span(group)
                    begin += pos
                    end += pos
                    assert begin >= 0
                    assert end >= 0
                    result += string[begin:end]
                result += s[1:]
            else:
                result += s
        return result

    def gsub_regexp_block(self, space, block, w_match):
        w_arg = space.send(w_match, space.newsymbol("[]"), [space.newint(0)])
        return self.gsub_yield_block(space, block, w_arg)

    def gsub_regexp_hash(self, space, w_hash, w_match):
        w_arg = space.send(w_match, space.newsymbol("[]"), [space.newint(0)])
        return self.gsub_lookup_hash(space, w_hash, w_arg)

    def gsub_string(self, space, w_pattern, replacement, w_hash, block, first_only):
        result = []
        pos = 0
        string = space.str_w(self)
        pattern = space.str_w(w_pattern)
        while pos + len(pattern) < len(string):
            idx = string.find(pattern, pos)
            if idx >= 0:
                result += string[pos:idx]
                if replacement is not None:
                    result += replacement
                elif block:
                    result += self.gsub_yield_block(space, block, w_pattern)
                elif w_hash:
                    result += self.gsub_lookup_hash(space, w_hash, w_pattern)
                pos = idx + len(pattern)
            else:
                break
            if first_only:
                break
        result += string[pos:]
        return space.newstr_fromchars(result)

    def gsub_yield_block(self, space, block, w_matchstr):
        w_value = space.invoke_block(block, [w_matchstr])
        return self.gsub_replacement_to_s(space, w_value)

    def gsub_lookup_hash(self, space, w_hash, w_matchstr):
        w_value = space.send(w_hash, space.newsymbol("[]"), [w_matchstr])
        return self.gsub_replacement_to_s(space, w_value)

    def gsub_replacement_to_s(self, space, w_replacement):
        if space.is_kind_of(w_replacement, space.w_string):
            return space.str_w(w_replacement)
        else:
            w_replacement = space.send(w_replacement, space.newsymbol("to_s"))
            if space.is_kind_of(w_replacement, space.w_string):
                return space.str_w(w_replacement)
            else:
                return space.any_to_s(w_replacement)

    @classdef.method("chomp!")
    def method_chomp_i(self, space, w_newline=None):
        if w_newline is None:
            w_newline = space.globals.get(space, "$/")
        if w_newline is space.w_nil:
            return self
        newline = space.str_w(space.convert_type(w_newline, space.w_string, "to_str"))
        if newline in "\n\r":
            newline = None
        self.strategy.to_mutable(space, self)
        changed = self.strategy.chomp(self.str_storage, newline)
        return self if changed else space.w_nil

    @classdef.method("chop!")
    def method_chop_i(self, space):
        self.strategy.to_mutable(space, self)
        changed = self.strategy.chop(self.str_storage)
        return self if changed else space.w_nil

    @classdef.method("reverse!")
    def method_reverse_i(self, space):
        self.strategy.to_mutable(space, self)
        self.strategy.reverse(self.str_storage)
        return self

    @classdef.method("next!")
    @classdef.method("succ!")
    def method_succ_i(self, space):
        self.strategy.to_mutable(space, self)
        self.strategy.succ(self.str_storage)
        return self

    @classdef.method("insert", index="int", other="str")
    @check_frozen()
    def method_insert(self, space, index, other):
        if index < 0:
            index += self.length() + 1
        if not 0 <= index <= self.length():
            raise space.error(space.w_IndexError,
                "index %d out of string" % index
            )
        self.strategy.to_mutable(space, self)
        self.strategy.insert(self.str_storage, index, other)
        return self