I've posted a while back a string=>string substring function that doesn't allocating: google

"nonallocating unicode string manipulations"

code:

auto slice(T)(T a,size_t u, size_t v)if(is(T==string)){//TODO:generalize to isSomeString

import std.exception;

auto m=a.length;

size_t i;

enforce(u<=v);

import std.utf;

while(u-- && i<m){

auto si=stride(a,i);

i+=si;

v--;

}

// assert(u==-1);

// enforce(u==-1);

size_t i2=i;

while(v-- && i2<m){

auto si=stride(a,i2);

i2+=si;

}

// assert(v==-1);

enforce(v==-1);

return a[i..i2];

}

unittest{

import std.range;

auto a="≈açç√ef";

auto b=a.slice(2,6);

assert(a.slice(2,6)=="çç√e");

assert(a.slice(2,6).ptr==a.slice(2,3).ptr);

assert(a.slice(0,a.walkLength) is a);

import std.exception;

assertThrown(a.slice(2,8));

assertThrown(a.slice(2,1));

}

On Sat, Oct 26, 2013 at 3:17 PM, Ali Çehreli <acehreli@yahoo.com> wrote:

On 10/26/2013 02:25 PM, Namespace wrote:

On Saturday, 26 October 2013 at 21:23:13 UTC, Gautam Goel wrote:

Dumb Newbie Question: I've searched through the library reference, but
I haven't figured out how to extract a substring from a string. I'd
like something like string.substring("Hello", 0, 2) to return "Hel",
for example. What method am I looking for? Thanks!

Use slices:

string msg = "Hello";
string sub = msg[0 .. 2];

Yes but that works only if the string is known to contain only ASCII codes. (Otherwise, a string is a collection of UTF-8 code units.)

I could not find a subString() function either but it turns out to be trivial to implement with Phobos:

import std.range;
import std.algorithm;

auto subRange(R)(R s, size_t beg, size_t end)
{
return s.dropExactly(beg).take(end - beg);
}

unittest
{
assert("abcçdef".subRange(2, 4).equal("cç"));
}

void main()
{}

That function produces a lazy range. To convert it eagerly to a string:

import std.conv;

string subString(string s, size_t beg, size_t end)
{
return s.subRange(beg, end).text;
}

unittest
{
assert("Hello".subString(0, 2) == "He");
}

Ali