Vector swizzles in D

module main;

import std.stdio;
import std.process;
import std.conv;

private immutable (char[][]) elementNames = [['x', 'y', 'z', 'w'], ['r', 'g', 'b', 'a'], ['s', 't', 'p', 'q']];

int main(string[] argv) {
    alias Vec!4 Vec4;

    Vec4 v = Vec4(1, 2, 3, 4);

    writeln(v.bgra); // Prints Vec!(4)([3, 2, 1, 4])
    writeln(v.rg); // Prints Vec!(2)([1, 2])

    return 0;
}

struct Vec(size_t size) {
    alias size Size;

    mixin(generateConstructor(Size));

    mixin(generateProperties(Size));

    auto opDispatch(string s)() {
        mixin(generateSwizzle(s));
    }

    float v[Size];
}

private string generateConstructor(size_t size) {
    string constructorParams;
    string constructorBody;

    foreach(i; 0..size) {
        string paramName = "v" ~ to!string(i);
        constructorParams ~= "float " ~ paramName ~ "=0,";
        constructorBody ~= "v[" ~ to!string(i) ~ "] = " ~ paramName ~ ";";
    }

    return "this(" ~ constructorParams[0..$-1] ~ "){" ~ constructorBody ~ "}";
}

private string generateProperties(size_t size) {
    string props;

    foreach(names; elementNames) {
        foreach(i, name; names[0..size]) {
            props ~= "@property float " ~ name ~ "() const { return v[" ~ to!string(i) ~ "]; }";
            props ~= "@property void " ~ name ~ "(float f) { v[" ~ to!string(i) ~ "] = f; }";
        }
    }

    return props;
}

private string generateSwizzle(string elements) {
    string swizzleImpl = "return Vec!" ~ to!string(elements.length) ~ "(";

    foreach(e; elements) {
        swizzleImpl ~= e ~ ",";
    }

    return swizzleImpl[0..$-1] ~ ");";
}