Custom opCmp for struct array sort

[bearophile]

New:
> When I sort these paths, in the case of symlinks I want to ignore the right hand side and I just use the path before the "=" sign.

This may work (D1), I have cleaned up your code some:

import std.string: find, cmp;
import std.stdio: writefln;

struct Path {
    string thePath;

    int opCmp(Path other) {
        int pos;
        string a, b;

        pos = find(this.thePath, "=");
        if (pos > -1)
            a = this.thePath[0 .. pos];
        else
            a = this.thePath;

        pos = find(other.thePath, "=");
        if (pos > -1)
            b = other.thePath[0 .. pos];
        else
            b = other.thePath;

        return cmp(a, b);
    }
}

void main() {
    string[][Path] contents = [
        Path("/002=/other_dir"): ["aa","bb","cc","dd"],
        Path("/001"): ["aa","bb","cc","dd"],
        Path("/002=/hello") : ["aa","bb","cc","dd"]
    ];

    foreach (item; contents.keys.sort)
        writefln(item.thePath);
}

Note that you may not need it, because the part before = is on the left, so just sorting the strings may give you the order you need, without using any opCmp.

For other similar questions the D.learn newsgroup is fitter.

Bye,
bearophile