== returns false for apparently equal strings

[quanglewangle]

namespace TRYOUT is
use System;
use Generic;

class Main is

// class Main is

    init() is
        var s1 = "abcd";
        var s2 = "b";

        IO.Std.out.println ("substring:" + s1.substring(1,2) + " s2: " + s2);

        if s1.substring(1,2) == s2 then
            IO.Std.out.println("hit");
        else
            IO.Std.out.println(">" + s1.substring(1,2) + "< should be equal to >" + s2 + "< but isn't");
        fi
    si
si

si

[quanglewangle]

Oops! should have been using =~

[degory]

Behaviour of == is similar to Java - for reference types it compares for reference equality only.

=~ is the overridable equality operator, and is defined by the L library for strings, returning true if the strings represent exactly equal sequences of bytes.

Only=~ can be defined, x !~ y returns, by definition, !(x =~ y). This behaviour cannot be overridden.

=~ and !~ are defensive against nulls and will never call the user operator method with a null argument. The compiler generates code around uses of =~ and !~ such that:

null =~ null
null !~ anything-non-null
anything-non-null !~ null'

without actually calling =~, for both constant and run-time nulls