introduce a function to check whether a value can be represented as a type

[eschnett]

It would be nice if one could write x in Int32 etc. to check whether the value of x can be represented as Int32. This would be implemented as

in(x::Real, ::Type{T}) where {T<:Real} = x in typemin(T):typemax(T)

mimicking in(x::Real, r::AbstractRange{<:Real}).

Note that this is different from x isa Int32, which checks the type of x, not its value.

[mbauman]

I'm having a hard time understanding what this might mean in general. Is [1,2,3] in UnitRange{Int}? Is (a=2, b=3) in Dict{Symbol, Int}? is "this" in Any? What if I pass a Union?

[jishnub]

For the first example, one may use typemin(Int32) <= x <= typemax(Int32) to check if it lies in range.

[eschnett]

I'm imagining types that implement typemin and typemax, thus Any wouldn't be a valid second argument (although that might work too). Thus UnitRange also wouldn't be valid.

My starting point is that types are very similar to set of values, and thus in makes sense.

Maybe "can be converted to" would be another way of thinking about this.

[mbauman]

But it's gotta consider more than just typemin and typemax — T<:Real also includes rationals and floating points and unions thereof (and your current definition is wrong for those).

My point is more general than the examples I gave — in works on values and collections of values, and checks if any value is equal to one in the collection. This is implicitly considering types as a collection of values and there does exist a UnitRange that is equal to [1,2,3].

This could be a useful operation to have, but I don't think it should be called in, and I think it's gotta carefully consider what the generic behavior and definition would be.

[ararslan]

Perhaps this would be a natural extension of isvalid(T, value), which is currently defined only for T as String or Char.