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Advanced Programming Techniques in D

static foreach

Explore the static foreach feature in D programming to understand how it unrolls loops at compile time with more flexibility than compile-time foreach. Learn its applications with any compile-time ranges, module scope usage, and how it handles loop control statements for efficient code generation.

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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, ...