return type of ceil and floor

[Gabor]

The return type of the ceil and floor functions seem to depend on the argument type.

 

Is this the intended behaviour?

 

> ceil(5)
5
> ceil(10/2)
5.0
> typeof(ceil(5))
Int32
> typeof(ceil(10/2))
Float64

 

[Tim Holy]

On Thursday, May 02, 2013 12:49:42 AM Gabor wrote:
> The return type of the ceil and floor functions seem to depend on the
> argument type.
>
> Is this the intended behaviour?

Yes. But from your question, I bet what you're looking for is iceil() and
ifloor().

--Tim

[Gabor]

Hi Tim,

 

I know iceil() and ifloor(),

they work consistently and according to the documentation.

 

However, for ceil() and floor() the documentation says:

ceil(x[, digits[, base]]) → FloatingPoint¶

floor(x[, digits[, base]]) → FloatingPoint¶

 

An integer return type is clearly not a FloatingPoint,

so either the documentation is wrong,

or (as I suspect) this is not the intended behaviour.

 

Gabor

[Stefan Karpinski]

The documentation is wrong here. The idea is that ceil and floor return a value that is the same type as x, which is often faster and/or better for the type stability of the ongoing computation (and is also what the functions of the same name do in C).

[Stefan Karpinski]

For what it's worth, I really dislike the type annotations in the manual. Generic functions are about a concept and the documented types are usually wrong even in base and also since it's expected that people extend generic functions to other types they are inherently wrong. It's a little unusual, but Julia's documentation for generic functions must be about what *concept* a function implements, not just the specific methods that Base happens to provide. That way others can understand how their extensions of these functions should work. Of course, documenting a concept is much harder than just describing what something does.

[Stefan Karpinski]

Also, I fixed this: http://docs.julialang.org/en/latest/stdlib/base/#Base.round

[Gabor]

 

Stefan, thanks for the explanation and the documentation fix.