Document numeric conversions

[ArchRobison]

It seems that the Julia documentation does not cover numeric conversions. I think the subject deserves mention as a section of Mathematical Operations and Elementary Functions, with cross references between it and the Conversion and Promotion chapter.

How many forms should it cover? The three forms I find myself using are:

• Int(x) - checked for exactness, i.e. value preserving
• x % Int - modular, restricted to integer types
• floor( Int, x ) - checked for exactness after flooring (and is documented)

I would describe the three forms and their tradeoffs. Any others worth documenting in said section of the manual?

[simonbyrne]

There is also convert, but I'm not sure what the distinction is between T(x) and convert(T,x)?

[simonbyrne]

Also, unsafe_trunc.

[swt30]

There's also the safe form trunc which checks that it's representable in the new type.

T(x) calls the constructor for type T with value x. If a constructor isn't defined, it falls back to convert(T, x) as of version 0.4, which means you can write things like Float32(1), which is nice and compact. I'm not really sure what to write for custom types though (numeric or otherwise). Do I define

• the constructor T(x)?
• the function call(::Type{T}, x)?
• or convert(::Type{T}, x)?

[simonbyrne]

The first 2 are actually the same (the call function was a design hack to get inability to define constructors for bits types: this may change in future).

I would suggest defining convert, but this is a good question.

[brenhinkeller]

Looks like the current (1.8.3) section on Mathematical Operations and Elementary Functions has a whole subsection on Numerical Conversions, so I think we can consider this completed!