What's the preferred way to substring in D language?

Question

I have googled but just no luck.

I want to chop the first character of a string like this:

string s = "hello, world";
string t = cast(string) s[1..$];  // OK
string u = s[1..$]; // ERROR, can't cast char[] to string.

Well, I may miss something. cast(string) make the code more unreadable.

Is there any easier way to get the substring (without cast)?

Answer 1

You shouldn't have to cast there at all, these are all strings.

If s is a char[], you might be able to force it to be string by specifying it (like you did in the example), or use to!string(s) to convert it. to!string is found in the module std.conv.

After you have everything of consistent types, when doing substrings, slicing is good, like you are doing there, but you might want to be a little careful if there's non-ascii characters in it. string[1 .. $] chops off the first byte, but a character might be multiple bytes.

If you import std.utf;, you'll have a function called stride available which can check for multi byte characters.

string t = s[s.stride() .. $]; // chops off the first character*, even if it is multi-byte

• Note that I'm saying "character" here but technically, that's not always true either. Unicode strings can get very complicated. std.uni.normalize is a function that can help this, but it still isn't perfect, slicing off one character depends on your specific task.

Generally, though, I'd say get the index with other functions, then slice it. So if you want to substring world, do:

import std.string;
auto index = s.indexOf("world");
if(index == -1) throw new Exception("substring 'world' not found");

auto world = s[index .. $]; // gets the substring starting from world to the end of string

Functions like indexOf can handle the complications of multi-byte characters for you.