What should be reterned by std.array.replaceFirst

[zhang]

I tested std.array.replaceFirst with the code belown:

    string s1 = "abc bcf";

    string s2 = s1.replaceFirst("bc", "ee");
    writefln("%s\n%s", s1, s2);

and got s2 is "aee". Should it be "aee bcf"?

Is it a bug, or just it is that?

Thanks.
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Zhang <bitworld at qq.com>