Traits

Syntax#

__traits (TraitsKeyword, TraitsArguments…)

Iterating over the members of a struct

import std.stdio;

struct A {
    int b;
    void c();
    string d;
};

void main() {
    // The following foreach is unrolled in compile time
    foreach(name; __traits(allMembers, A)) {
        pragma(msg, name);
    }
}

The allMembers traits returns a tuple of string containing the names of the members of the given type. These strings are known at compile time.

Iterating over members of a struct/class without their inherited members

module main;

auto getMemberNames(T)() @safe pure {
    string[] members;
    
    foreach (derived; __traits(derivedMembers, T)) {
        members ~= derived;
    }
    
    return members;
}

class Foo {
    int a;
    int b;
}

class Bar : Foo {
    int c;
    int d;
    int e;
}

void main() {
    import std.stdio;
    
    foreach (member; getMemberNames!Bar) {
        writeln(member);
    }
}

derivedMembers returns a tuple of string literals, where each string is the member name.

The example outputs:

c
d
e