Add single argument version of isapprox (#32305)

Adds a single argument version of isapprox or ≈, in the same vein as the single argument version of `==`.

NEWS.md

@@ -53,6 +53,7 @@ New library features
 --------------------
 * Function composition now works also on one argument `∘(f) = f` (#34251)
 
+* `isapprox` (or `≈`) now has a one-argument "curried" method `isapprox(x)` which returns a function, like `isequal` (or `==`)` ([#32305]).
 * `Ref{NTuple{N,T}}` can be passed to `Ptr{T}`/`Ref{T}` `ccall` signatures ([#34199])
 
 

base/floatfuncs.jl

@@ -274,6 +274,15 @@ function isapprox(x::Number, y::Number; atol::Real=0, rtol::Real=rtoldefault(x,y
     x == y || (isfinite(x) && isfinite(y) && abs(x-y) <= max(atol, rtol*max(abs(x), abs(y)))) || (nans && isnan(x) && isnan(y))
 end
 
+"""
+    isapprox(x; kwargs...) / ≈(x; kwargs...)
+
+Create a function that compares its argument to `x` using `≈`, i.e. a function equivalent to `y -> y ≈ x`.
+
+The keyword arguments supported here are the same as those in the 2-argument `isapprox`.
+"""
+isapprox(y; kwargs...) = x -> isapprox(x, y; kwargs...)
+
 const ≈ = isapprox
 """
     x ≉ y

test/floatfuncs.jl

@@ -100,3 +100,9 @@ end
     @test round(Float16(0.6), sigdigits=2) === Float16(0.6)
     @test round(Float16(1.1), sigdigits=70) === Float16(1.1)
 end
+
+@testset "curried approximation" begin
+
+    @test ≈(1.0; atol=1).(1.0:3.0) == [true, true, false]
+
+end