I'm writing a script type like std::optional<T>. I've seen the document saying that the bool opImplConv() won't be used because of ambiguity. But I think it can use bool opConv() to convert the result of expression to bool. The if statement itself is enough to consider the user needs a explicit conversion. This is exactly how C++ deal with non-bool result in a if condition, it will invoke the operator bool() of that type even if it is declared as explicit operator bool().

If this feature can be implemented, I can write script like this

optional<string> opt_str = "test";
if(opt_str)
	// ...

instead of

optional<string> opt_str = "test";
if(bool(opt_str))
	// ...

HenryAWE said:

optional<string> opt_str = "test";
if(opt_str)
	// ...

What would the result for that be? “test” is neither true nor false 🙂

I will eventually get to implementing an engine property to allow the application to set whether or not conversion to bool should be done implicitly. It is not a high priority for me though.

Should someone (*hint*) provide the patch for it I'd gladly incorporate it into the repository though.

Maybe the code fragment above is not clear. The optional manages a value that may or may not exists (Introduction of the optional in C++17). For example, it is useful to implement a optional<T> find(const string&in key) method of a dictionary-like object. The optional can be converted to bool to check if the optional contains value. Here is a detailed script example:

optional<int> empty_opt;
if(empty_opt) // `bool(empty_opt)` or `empty_opt.has_value()` in current version of AS
    do_something(empty_opt.value); // Won't be executed
    
optional<int> non_empty_opt = 42;
if(non_empty_opt)
    do_something(non_empty_opt.value); // Will be executed

WitchLord said:

Should someone (*hint*) provide the patch for it I'd gladly incorporate it into the repository though.

After a glance at the source code of AS, I guess this behavior is controlled by the asCCompiler::CompileIfStatement in source/as_compiler.cpp. Maybe I can try to implement something like a engine property named asEP_EXPLICIT_BOOL_CONV_IN_CONDITION?

Give it a shot. 🙂

I can make the final adjustments if needed.

If I understand the code correctly, the only modification needs to be done inside the asCCompiler::CompileIfStatement is changing the 4th argument of ImplicitConversion from asIC_IMPLICIT_CAST to asIC_EXPLICIT_VAL_CAST if a certain engine property is set. I've walked through the source of asCCompiler::ImplicitConvObjectToPrimitive, and it seems that this function can also perform an explicit cast if a correct convType argument is passed. (The function name is quite confusing 😂)

If the above approach is correct, I will try to implement the engine property and corresponding test in this way.

In addition, how do I summit a patch? Should I just post (probably lengthy) svn diff result here, or send it by e-mail or something else?

You can send me the modified files via email. Either diff or complete files is ok, though I prefer the complete files.

Don't forget to provide the code for testing the changes as well, so I can merge that into the regression test suite.

@WitchLord The patch has been sent by email.