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Expose ComposedFunction as a public API #37517

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Sep 24, 2020
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Expose ComposedFunction as a public API #37517

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47802b1
document ComposedFunction
jw3126 Sep 10, 2020
40f3179
Update base/operators.jl
jw3126 Sep 10, 2020
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Update base/operators.jl
jw3126 Sep 10, 2020
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Update base/operators.jl
tkf Sep 10, 2020
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Update base/operators.jl
jw3126 Sep 10, 2020
feaf87f
add ComposedFunction to News.md
jw3126 Sep 10, 2020
d7195b8
Give more descriptive names to the fields of ComposedFunction
jw3126 Sep 10, 2020
400de93
Update base/operators.jl
tkf Sep 10, 2020
90e0015
export ComposedFunction
jw3126 Sep 16, 2020
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Merge branch 'doc_composition' of github.com:jw3126/julia into doc_co…
jw3126 Sep 16, 2020
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improve ComposedFunction docstring
jw3126 Sep 17, 2020
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improve ComposedFunction docstring
jw3126 Sep 17, 2020
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Merge branch 'master' into doc_composition
jw3126 Sep 20, 2020
3420ac6
fix ComposedFunction doctest
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Merge branch 'doc_composition' of github.com:jw3126/julia into doc_co…
jw3126 Sep 21, 2020
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1 change: 1 addition & 0 deletions NEWS.md
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Expand Up @@ -99,6 +99,7 @@ Standard library changes
* `RegexMatch` objects can now be probed for whether a named capture group exists within it through `haskey()` ([#36717]).
* For consistency `haskey(r::RegexMatch, i::Integer)` has also been added and returns if the capture group for `i` exists ([#37300]).
* A new standard library `TOML` has been added for parsing and printing [TOML files](https://toml.io) ([#37034]).
* The composition operator `∘` now returns a `Base.ComposedFunction` instead of an anonymous function ([#37517]).

#### LinearAlgebra
* New method `LinearAlgebra.issuccess(::CholeskyPivoted)` for checking whether pivoted Cholesky factorization was successful ([#36002]).
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44 changes: 36 additions & 8 deletions base/operators.jl
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Expand Up @@ -871,26 +871,54 @@ julia> fs = [
julia> ∘(fs...)(3)
3.0
```
See also [Base.ComposedFunction](@ref).
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"""
function ∘ end

struct ComposedFunction{F,G} <: Function
f::F
g::G
ComposedFunction{F, G}(f, g) where {F, G} = new{F, G}(f, g)
ComposedFunction(f, g) = new{Core.Typeof(f),Core.Typeof(g)}(f, g)
"""
Base.ComposedFunction{Outer,Inner} <: Function

Represents the composition of two callable objects `f::Outer` and `g::Inner`.
```jldoctest
julia> sin ∘ cos === Base.ComposedFunction(sin, cos)
true

julia> typeof(sin∘cos)
Base.ComposedFunction{typeof(sin), typeof(cos)}
```
The composed pieces are stored in the fields of `ComposedFunction` and can be retrieved as follows:
```jldoctest
julia> composition = sin ∘ cos
sin ∘ cos

julia> composition.outer === sin
true

julia> composition.inner === cos
true
```
!!! compat "Julia 1.6"
ComposedFunction requires at least Julia 1.6. In earlier version `∘` returns an anonymous function instead.

See also [`∘`](@ref).
"""
struct ComposedFunction{O,I} <: Function
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Hi, This is coming very late.

Just wanted to find out if it is necessary to restrict O and I to be subtypes of Base.Callable as in

struct ComposedFunction{O<:Base.Callable, I<:Base.Callable} <: Function

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There is no reason to restrict to Callable here. There are lots of callable objects that aren't a subtype of Callable and this would break those cases.

outer::O
inner::I
ComposedFunction{O, I}(outer, inner) where {O, I} = new{O, I}(outer, inner)
ComposedFunction(outer, inner) = new{Core.Typeof(outer),Core.Typeof(inner)}(outer, inner)
end

(c::ComposedFunction)(x...) = c.f(c.g(x...))
(c::ComposedFunction)(x...) = c.outer(c.inner(x...))

∘(f) = f
∘(f, g) = ComposedFunction(f, g)
∘(f, g, h...) = ∘(f ∘ g, h...)

function show(io::IO, c::ComposedFunction)
show(io, c.f)
show(io, c.outer)
print(io, " ∘ ")
show(io, c.g)
show(io, c.inner)
end

"""
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1 change: 1 addition & 0 deletions doc/src/base/base.md
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Expand Up @@ -237,6 +237,7 @@ Base.invokelatest
new
Base.:(|>)
Base.:(∘)
Base.ComposedFunction
```

## Syntax
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