Safe cast from int64 to int8

[DeusModus]

Hi!

Is there any possibility to cast int64 to int8 and retrieve error if int64 type val overflows int8?

[Josh Bleecher Snyder]

> Is there any possibility to cast int64 to int8 and retrieve error if int64
> type val overflows int8?

You can convert back and check whether the value was preserved.

http://play.golang.org/p/wnZj8n8Ply

-josh

[Ian Lance Taylor]

On Tue, Apr 7, 2015 at 9:12 AM, DeusModus <maxime...@gmail.com> wrote:
>
> Is there any possibility to cast int64 to int8 and retrieve error if int64
> type val overflows int8?

i8 := int8(i64)
if int64(i8) != i64 {
// oh noes!!!
}

Ian

[Joe Taber]

From the spec[1], "When converting between integer types... The conversion always yields a valid value; there is no indication of overflow."

You'll have to check afterwards as Josh or Ian mentioned.

[1]: https://golang.org/ref/spec#Conversions

[Axel Wagner]

Or you use the math-package: http://play.golang.org/p/kUTi4yzisV

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[DeusModus]

Thought that there was more elegant way.
Anyway, thank you guys.

PS: I'll write library for this purpose if there is no any.

[Konstantin Khomoutov]

Please, don't do that.
There's no need to write a library to provide a function implementing
three lines of code. Even if there will be N functions,
each implementing these three lines of code -- one for each integral
type. Functions might be not inlined for some reason and won't be
optimized. Another problem is dependencies. Please read [1] and watch
the video it refers to.

1. https://groups.google.com/d/msg/golang-nuts/R_lqsTTBh6I/DWIwfuMXjfgJ

[Klaus Post]

On Thursday, 9 April 2015 12:38:56 UTC+2, Konstantin Khomoutov wrote:

Please, don't do that.

Why not - then 4 lines of code will become much shorter.. something like 4 lines of code ;)

Seriously, though, look at how you will likely use it in your actual code. As you can see you don't really gain anything, and you lose clarity of what happens in your code beside the inlining issue Konstantin pointed out.

 // Inline, 4 lines.
 if int64(int8(x)) != x {
   return ErrTruncated
 }
 v := int8(x)
 
 // With "package", 4 lines.
 v, err := caster.Int64ToInt8(x)
 if err != nil {
   return err
 }

 

[Dave Cheney]

Any Go programmer can read the first example with no training.

Only a Go programmer who has derailed themselves to looking up the documentation of your caster package.

Brevity is not a ends in itself.