Primitive parametric types

General Usage
1

Is it possible to specify the bit size of a primitive type as a parameter?
If I try:

primitive type MyType{B,T,D} <: Number B end

I get :

ERROR: invalid declaration of primitive type MyType

additionally, I would like to use the parameters T and D as a type and a constant respectively in methods that take MyType{B,T,D} as one of their arguments

2

No. And you wouldn’t really want to do that. You can have a primitive type that has a parameter; you cannot use the parameter to provide part of the primitive type’s specific definition. The parameter cannot be swallowed into the declaration of the type itself.

3

Actually, that is exactly what I wanted to do :slightly_smiling_face:
I don’t understand the problems involved with this.

If I could simplify the question. How about the following:

julia> primitive type MyType{T} <: Number sizeof(T)*8 end

julia> sizeof(MyType{UInt32})
24

julia> sizeof(UInt32)
4

This syntax does compile, however as you can see the number of bits is 24*8, and this is the same whatever T is.
Is there any way to declare primitive parametric types with varying sizes?

4

There is not because primitive types are used to generate the system level number types and if one could declare a primitive type, say Float64, with varying size … well that would lead to the possibility of Float64s with the precision of Float16s. (OK, I may be overstating this … essentially, though you should not conceptualize primitive types (parameterized or not) as if they were another sort of possibly parameterized struct.)

Two different phyla [if you happen to be a Bio person].

5

What is it that you intend to do with this – there may be a much better approach that gives the outcome you seek. Pretend you had that sort of type – how are you applying it and why – to what end?

6

@hros let me know … we’ll keep moving this forward.

you might use a parameterized struct and this package
https://github.com/vtjnash/ComputedFieldTypes.jl
(it does nothing with primitive types, but your struct field can be of a computed type).

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