proposal: strings: add a ReplaceRange function

[Mutoxicated]

Proposal Details

It's niche but it's nice when it's there.

[randall77]

We're going to need more detail than that.
What is the function signature? Argument/results types and names?
What is it supposed to do? A prototype go doc string would help.

[YkdWaWEzVmphR1Z1]

This is the rust version: https://doc.rust-lang.org/stable/std/string/struct.String.html#method.replace_range
So I guess, the function signature would be:

// Removes the range [i, j) and replaces it with new. Panics if the range is out of bounds.
func ReplaceRange(s, new string, i,  j int) string

[YkdWaWEzVmphR1Z1]

So it would be essentially slices.Replace for strings I guess.

[randall77]

You can just do s[:i] + new + s[j:], which is shorter and arguably clearer than strings.ReplaceRange(s, new, i, j).

[zigo101]

s[:i] + new + s[j:] needs 2 allocations, but ReplaceRange only needs one.

From performance views, the strings/bytes functions which need allocations should have a version with a writer parameter.
But Go often favors simplicity over efficiency.

[randall77]

s[:i] + new + s[j:] needs 2 allocations, but ReplaceRange only needs one.

I'm pretty sure the former needs only 1 allocation.

[zigo101]

I think producing new needs an extra allocation.

[YkdWaWEzVmphR1Z1]

He is referring to a compiler optimization,which may exist.

[YkdWaWEzVmphR1Z1]

This pattern is not very common, you need to index the string, so it is also not less error prone. Maybe the slices.Replace version makes more sense, since it less likely to be optimized.

[earthboundkid]

func sreplace(s, new string, i, j int) string {
	return s[:i] + new + s[j:]
}

var sink string

allocs := testing.AllocsPerRun(10, func() {
	sink = sreplace("Hello, world!", "W", 7, 8)
})

This is reporting 1 for me, although it could be an artifact of it s and new being constants.

[Mutoxicated]

We're going to need more detail than that. What is the function signature? Argument/results types and names? What is it supposed to do? A prototype go doc string would help.

func ReplaceRange(s, new string, i, j int) string {
    return s[:i] + new + s[j:]
}

My bad I didn't initially provide a prototype.

You can just do s[:i] + new + s[j:], which is shorter and arguably clearer than strings.ReplaceRange(s, new, i, j).

It might be shorter, however I would argue that ReplaceRange has way clearer intent than s[:i] + new + s[j:].

[YkdWaWEzVmphR1Z1]

func randString(n int) string {
	s := make([]byte, n)
	for i := range s {
		s[i] = rand.N(byte(127))

	}
	return string(s)
}
s := randString(20)
new := randString(5)

func sreplace(s string, i, j int, new ...string) string {
	r := s[:i]
	for _, n := range new {
		r += n
	}
	r += s[j:]
	return r
}

This performs actually 2 allocations, I guess you would have to use a string builder.