Type conversion between numeric types

[luketpickering]

In the README it mentions that conversion between int/floating cannot be done implicitly. Is this really not possible? If a user wants to set a starting position vector as the origin, having

[start]
position = [0,0,0]

fail to be read by toml::get<std::vector<double>>(start_table.at("position")) is quite frustrating. I appreciate that doing implicit lossy conversions (1.2 as an int for example) might be an implementation choice, but the inability to get 0 as a double seems to be a bit arbitrary. If it is technically possible but not something you feel the need to implement, then I might have a look.

Thanks for the great library!

[ToruNiina]

I basically agree with your point, it would be more useful if it can convert int64_t into float and vice versa. But there is a reason why it is not supported.

When we specify a type that does not require any type conversion, it returns a reference (like int64_t&) that enables us to modify the content through it.

int64_t& x = toml::find<int64_t>(input, "x");
x = 42; // overwrite "x" in `input`

But, it is not possible to bind int64_t as a reference to other type, like double&. double is one of the types that is contained in the internal storage of toml::value and does not require type conversion (if the toml::value contains Float value). So if double is specified as a template argument of toml::get, it should returns double&, for the sake of consistency. Here, if the value actually contains int64_t, we cannot bind it to double& and the return type must be double. The problem is that we cannot know the actual contained type before parsing a file. If we want to support conversion, the return type of toml::get (whether it is a reference or a value) should be determined after checking what value is contained, that means that the type should be changed at runtime, and it is impossible.

So the available options are

• returning a value by copy. conversion via toml::get becomes handy, but modification is impossible. (breaking change)
• returning a value by reference. conversion via toml::get has restriction, but modification is possible. (current implementation)
• returning a wrapper type that automatically casts a value in assignment operator, and making the code complicated. (breaking change)
• add a totally new function, that might be named as toml::as<T>, that always returns a value instead of reference. (minor update)

I think the most feasible option is the last one.

[luketpickering]

Understood, I hadn't appreciated the reference problem. To forge ahead, I worked around it in my code with a simple toml::find wrapper template that if the return type template std::is_floating_point<T>::value is true, then it uses a specialization that checks at runtime if the parsed type is_integer() with the toml::value methods and if it is does the conversion.

Your proposed solution sounds perfect though, thank you for taking the time to read and think about my question!

[xgdgsc]

Could it give a warning if a key exists but with wrong type?