This question has kind of been asked before but I feel the asker was hasty to call an answer correct when he never actually got a real answer. Maybe there is no reason why, and this needs to be put in the standard later, you tell me. What is the rationale to not allow overloading of C++ conversions operator with non-member functions
I'm looking for the specific reason for this not being allowed as part of the design of the current standard. Basically, when you overload a cast operator to define an implicit conversion between two types, this overloaded definition has to be a member of the class that you're converting from, and not something outside a class. The obvious problem is that if you have types that you really can't modify for some reason but you want to implicitly convert between them for the sake of simplicity of syntax (despite the evils of implicit conversion) or because you have a bunch of other code, standard or custom that relies on implicit conversion...you can't do that if you can't add appropriate implicit conversions to the classes, so you need to use workarounds like regular functions for conversion that you would wrap around what would otherwise be the convenience of implicit conversion.
Also, is it...really possible that there would be a computational overhead to add these conversions outside a class? The way I see it, it would be easy for a compiler to, when going through to figure out what functions are available, associate external implicit conversion functions with the class they convert from so that the code is executed like it were part of that class as far as efficiency goes. The only downside would be the extra work it has to do to make the initial association, which should be almost nothing.
I will not take "because the standard says so" or "because implicit conversions are bad" as an answer. Somebody surely had a reason when they wrote the actual standard.
(I'm not a huge expert, I'm still learning the language.)
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