/
encodable.rs
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/
encodable.rs
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// Copyright 2012-2013 The Rust Project Developers. See the COPYRIGHT
// file at the top-level directory of this distribution and at
// http://rust-lang.org/COPYRIGHT.
//
// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
// option. This file may not be copied, modified, or distributed
// except according to those terms.
/*!
The compiler code necessary to implement the `#[deriving(Encodable)]`
(and `Decodable`, in decodable.rs) extension. The idea here is that
type-defining items may be tagged with `#[deriving(Encodable, Decodable)]`.
For example, a type like:
```ignore
#[deriving(Encodable, Decodable)]
struct Node { id: uint }
```
would generate two implementations like:
```ignore
impl<S:serialize::Encoder> Encodable<S> for Node {
fn encode(&self, s: &S) {
s.emit_struct("Node", 1, || {
s.emit_field("id", 0, || s.emit_uint(self.id))
})
}
}
impl<D:Decoder> Decodable for node_id {
fn decode(d: &D) -> Node {
d.read_struct("Node", 1, || {
Node {
id: d.read_field("x".to_string(), 0, || decode(d))
}
})
}
}
```
Other interesting scenarios are whe the item has type parameters or
references other non-built-in types. A type definition like:
```ignore
#[deriving(Encodable, Decodable)]
struct spanned<T> { node: T, span: Span }
```
would yield functions like:
```ignore
impl<
S: Encoder,
T: Encodable<S>
> spanned<T>: Encodable<S> {
fn encode<S:Encoder>(s: &S) {
s.emit_rec(|| {
s.emit_field("node", 0, || self.node.encode(s));
s.emit_field("span", 1, || self.span.encode(s));
})
}
}
impl<
D: Decoder,
T: Decodable<D>
> spanned<T>: Decodable<D> {
fn decode(d: &D) -> spanned<T> {
d.read_rec(|| {
{
node: d.read_field("node".to_string(), 0, || decode(d)),
span: d.read_field("span".to_string(), 1, || decode(d)),
}
})
}
}
```
*/
use ast;
use ast::{MetaItem, Item, Expr, ExprRet, MutMutable, LitNil};
use codemap::Span;
use ext::base::ExtCtxt;
use ext::build::AstBuilder;
use ext::deriving::generic::*;
use parse::token;
pub fn expand_deriving_encodable(cx: &mut ExtCtxt,
span: Span,
mitem: @MetaItem,
item: @Item,
push: |@Item|) {
let trait_def = TraitDef {
span: span,
attributes: Vec::new(),
path: Path::new_(vec!("serialize", "Encodable"), None,
vec!(box Literal(Path::new_local("__S")),
box Literal(Path::new_local("__E"))), true),
additional_bounds: Vec::new(),
generics: LifetimeBounds {
lifetimes: Vec::new(),
bounds: vec!(("__S", ast::StaticSize, vec!(Path::new_(
vec!("serialize", "Encoder"), None,
vec!(box Literal(Path::new_local("__E"))), true))),
("__E", ast::StaticSize, vec!()))
},
methods: vec!(
MethodDef {
name: "encode",
generics: LifetimeBounds::empty(),
explicit_self: borrowed_explicit_self(),
args: vec!(Ptr(box Literal(Path::new_local("__S")),
Borrowed(None, MutMutable))),
ret_ty: Literal(Path::new_(vec!("std", "result", "Result"),
None,
vec!(box Tuple(Vec::new()),
box Literal(Path::new_local("__E"))),
true)),
attributes: Vec::new(),
const_nonmatching: true,
combine_substructure: combine_substructure(|a, b, c| {
encodable_substructure(a, b, c)
}),
})
};
trait_def.expand(cx, mitem, item, push)
}
fn encodable_substructure(cx: &mut ExtCtxt, trait_span: Span,
substr: &Substructure) -> @Expr {
let encoder = substr.nonself_args[0];
// throw an underscore in front to suppress unused variable warnings
let blkarg = cx.ident_of("_e");
let blkencoder = cx.expr_ident(trait_span, blkarg);
let encode = cx.ident_of("encode");
return match *substr.fields {
Struct(ref fields) => {
let emit_struct_field = cx.ident_of("emit_struct_field");
let mut stmts = Vec::new();
let last = fields.len() - 1;
for (i, &FieldInfo {
name,
self_,
span,
..
}) in fields.iter().enumerate() {
let name = match name {
Some(id) => token::get_ident(id),
None => {
token::intern_and_get_ident(format!("_field{}",
i).as_slice())
}
};
let enc = cx.expr_method_call(span, self_, encode, vec!(blkencoder));
let lambda = cx.lambda_expr_1(span, enc, blkarg);
let call = cx.expr_method_call(span, blkencoder,
emit_struct_field,
vec!(cx.expr_str(span, name),
cx.expr_uint(span, i),
lambda));
// last call doesn't need a try!
let call = if i != last {
cx.expr_try(span, call)
} else {
cx.expr(span, ExprRet(Some(call)))
};
stmts.push(cx.stmt_expr(call));
}
// unit structs have no fields and need to return Ok()
if stmts.is_empty() {
let ret_ok = cx.expr(trait_span,
ExprRet(Some(cx.expr_ok(trait_span,
cx.expr_lit(trait_span, LitNil)))));
stmts.push(cx.stmt_expr(ret_ok));
}
let blk = cx.lambda_stmts_1(trait_span, stmts, blkarg);
cx.expr_method_call(trait_span,
encoder,
cx.ident_of("emit_struct"),
vec!(
cx.expr_str(trait_span, token::get_ident(substr.type_ident)),
cx.expr_uint(trait_span, fields.len()),
blk
))
}
EnumMatching(idx, variant, ref fields) => {
// We're not generating an AST that the borrow checker is expecting,
// so we need to generate a unique local variable to take the
// mutable loan out on, otherwise we get conflicts which don't
// actually exist.
let me = cx.stmt_let(trait_span, false, blkarg, encoder);
let encoder = cx.expr_ident(trait_span, blkarg);
let emit_variant_arg = cx.ident_of("emit_enum_variant_arg");
let mut stmts = Vec::new();
let last = fields.len() - 1;
for (i, &FieldInfo { self_, span, .. }) in fields.iter().enumerate() {
let enc = cx.expr_method_call(span, self_, encode, vec!(blkencoder));
let lambda = cx.lambda_expr_1(span, enc, blkarg);
let call = cx.expr_method_call(span, blkencoder,
emit_variant_arg,
vec!(cx.expr_uint(span, i),
lambda));
let call = if i != last {
cx.expr_try(span, call)
} else {
cx.expr(span, ExprRet(Some(call)))
};
stmts.push(cx.stmt_expr(call));
}
// enums with no fields need to return Ok()
if stmts.len() == 0 {
let ret_ok = cx.expr(trait_span,
ExprRet(Some(cx.expr_ok(trait_span,
cx.expr_lit(trait_span, LitNil)))));
stmts.push(cx.stmt_expr(ret_ok));
}
let blk = cx.lambda_stmts_1(trait_span, stmts, blkarg);
let name = cx.expr_str(trait_span, token::get_ident(variant.node.name));
let call = cx.expr_method_call(trait_span, blkencoder,
cx.ident_of("emit_enum_variant"),
vec!(name,
cx.expr_uint(trait_span, idx),
cx.expr_uint(trait_span, fields.len()),
blk));
let blk = cx.lambda_expr_1(trait_span, call, blkarg);
let ret = cx.expr_method_call(trait_span,
encoder,
cx.ident_of("emit_enum"),
vec!(
cx.expr_str(trait_span, token::get_ident(substr.type_ident)),
blk
));
cx.expr_block(cx.block(trait_span, vec!(me), Some(ret)))
}
_ => cx.bug("expected Struct or EnumMatching in deriving(Encodable)")
};
}