EltypeExtensions.jl

EltypeExtensions.jl is a mini toolbox for eltype-related conversions. The motivation of this package comes from manipulating (nested) arrays with different eltypes. However if you have any reasonable idea that works on other instances, feel free to write an issue/pull request.

We note that this package has some overlap with TypeUtils.jl and Unitless.jl.

Introduction

elconvert

elconvert(T, x) works like convert(T, x), except that T refers to the eltype of the result. This can be useful for generic codes.

basetype and precisiontype

The basetype is used for nested collections, where eltype is repeatedly applied until the bottom. precisiontype has a similar idea, but goes deeper when possible. precisiontype is used to manipulate the accuracy of (nested) collections.

julia> basetype(Set{Matrix{Vector{Matrix{Complex{Rational{Int}}}}}})Complex{Rational{Int64}}
julia> precisiontype(Set{Matrix{Vector{Matrix{Complex{Rational{Int}}}}}})Rational{Int64}

Method naming convention

• sometype(T) gets the sometype of type T.
• sometype(x) = sometype(typeof(x)) is also provided for convenience.
• _to_sometype(T,S) converts the type S to have the sometype of T.
• someconvert(T,A) converts A to have the sometype of T.

where some can be el, base and precision.

On precisionconvert

precisionconvert accepts an optional third argument prec.

• When T has static precision, prec has no effect.
• When T has dynamic precision, prec specifies the precision of conversion. When prec is not provided, the precision is decided by the external setup from T. The difference is significant when precisionconvert is called by another function:

  julia> precision(BigFloat)256
  julia> f(x) = precisionconvert(BigFloat, x, 256)f (generic function with 1 method)
  julia> g(x) = precisionconvert(BigFloat, x)g (generic function with 1 method)
  julia> setprecision(128)128
  julia> f(π) # static precision3.141592653589793238462643383279502884197169399375105820974944592307816406286198
  julia> g(π) # precision varies with the global setting3.141592653589793238462643383279502884195

• When T is an integer, the conversion will dig into Rational as well. In contrast, since Rational as a whole is more "precise" than an integer, precisiontype doesn't unwrap Rational.

  julia> precisiontype(precisionconvert(Int128, Int8(1)//Int8(2)))Rational{Int128}