use generics in random

[ringabout]

Ref timotheecour#408

[Araq]

What about this remark? Shouldn't we keep it?

[ringabout]

It is already kept

Nim/lib/pure/random.nim

Line 264 in de29bed

## This proc uses the default random number generator. Thus, it is **not**

rand(max: float) already has the same comments and this generic procs reuse that commentbefore.

[timotheecour]

this comment is redundant (and only approximately correct) and should be removed, it's already specified what T is in the generated docs:

furthermore, Ordinal is clickable (thanks to docgen) so users who see Ordinal for the 1st time can just click to see the definition, which is explained in 1 place, where it belongs (https://nim-lang.github.io/Nim/system.html#Ordinal) => "1 definition rule" for docs

note that the definition for https://nim-lang.github.io/Nim/system.html#Ordinal should be fixed via s/enums/enums without holes/ but that's a separate issue

[timotheecour]

s/random floating point number/random number/

[timotheecour]

@xflywind thanks for tackling this; but this needs more care:

when defined case1:
  import std/random
  when defined case1a:
    # Error: type mismatch: got <Rand, Foo>
    type Fooa = enum k0,k1,k2
    echo rand(Fooa.high)
  when defined case1b:
    # Error: type mismatch: got <Rand, Dollar>
    type Dollar = distinct int
    echo rand(int.high.Dollar)
  when defined case1c: # ok
    echo rand(int64.high)
  when defined case1d:
    # Error: unhandled exception: value out of range [RangeDefect]
    echo rand(uint64.high)
  when defined case1e:
    # Error: type mismatch: got <Rand, char>
    echo (rand(char.high),)

in particular this should also be updated to be made generic:

proc rand*(r: var Rand; max: Natural): int {.benign.} =

and you can move the old underlying proc rand*(r: var Rand; max: Natural): int {.benign.} = implementation to some

proc randImpl(r: var Rand; max: Natural): int {.benign.} = ...

[timotheecour]

cast to avoid overflow errors