Advanced Programming Techniques in D/

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static foreach

static foreach

Learn about the static foreach loop and how it is a more powerful compile-time feature than foreach.

We'll cover the following...

You saw compile-time foreach earlier in the tuples chapter. Compile-time foreach iterates the loop at compile-time and unrolls each iteration as separate pieces of code. For example, consider the following foreach loop over a tuple:

D
import std.stdio;

import std.typecons;



void main() {

    auto t = tuple(42, "hello", 1.5);



    foreach (i, member; t) {

        writefln("%s: %s", i, member); 

    }

}

The compiler unrolls the loop similar to the following equivalent code:

D
{

    enum size_t i = 0; 

    int member = t[i]; 

    writefln("%s: %s", i,member);

}

{

    enum size_t i = 1; 

    string member = t[i]; 

    writefln("%s: %s", i, member);

}

{

    enum size_t i = 2; 

    double member = t[i]; 

    writefln("%s: %s", i, member);

}

Although very powerful, some properties of compile-time foreach may not be suitable in some cases:

  • With compile-time foreach, each unrolling of the loop introduces a scope. As seen with the i and member variables above, ...