Fix StackOverflowError when left and right do not promote to common type

This was adopted from AxisArrays

Author: timholy

src/IntervalSets.jl

@@ -13,4 +13,8 @@ include("closed.jl")
 ordered{T}(a::T, b::T) = ifelse(a < b, (a, b), (b, a))
 ordered(a, b) = ordered(promote(a, b)...)
 
+checked_conversion{T}(::Type{T}, a, b) = _checked_conversion(T, convert(T, a), convert(T, b))
+_checked_conversion{T}(::Type{T}, a::T, b::T) = a, b
+_checked_conversion{T}(::Type{T}, a, b) = throw(ArgumentError("$a and $b are not both of type $T"))
+
 end # module

src/closed.jl

@@ -5,9 +5,20 @@ mathematical notation, the constructed range is `[left, right]`.
 immutable ClosedInterval{T}
     left::T
     right::T
+
+    ClosedInterval(l::T, r::T) = new(l, r)
 end
 
-ClosedInterval(left, right) = ClosedInterval(promote(left, right)...)
+ClosedInterval{T}(left::T, right::T) = ClosedInterval{T}(left, right)
+(::Type{ClosedInterval{T}}){T}(left, right) =
+    ClosedInterval{T}(checked_conversion(T, left, right)...)
+
+function ClosedInterval(left, right)
+    # Defining this as ClosedInterval(promote(left, right)...) has one problem:
+    # if left and right do not promote to a common type, it triggers a StackOverflow.
+    T = promote_type(typeof(left), typeof(right))
+    ClosedInterval{T}(checked_conversion(T, left, right)...)
+end
 
 ..(x, y) = ClosedInterval(x, y)
 

test/runtests.jl

@@ -8,6 +8,7 @@ using Base.Test
     @test ordered(Float16(1), 2) == (1, 2)
 
     @testset "Closed Sets" begin
+        @test_throws ArgumentError :a .. "b"
         I = 0..3
         print(io, I)
         @test String(io) == "0..3"