Add only as replacement for convert

Author: pabloferz

docs/src/index.md

@@ -263,6 +263,7 @@ Open
 Unbounded
 first
 last
+only
 span
 isclosed
 isopen

src/Intervals.jl

@@ -10,6 +10,11 @@ using Dates: AbstractDateTime, value, coarserperiod
 
 import Base: ⊆, ⊇, ⊈, ⊉, union, union!, merge
 
+# Extend `Base.only` when it exists
+if VERSION >= v"1.4.0-DEV.142"
+    import Base: only
+end
+
 # Extend `Base.isdisjoint` when it exists
 # https://github.com/JuliaLang/julia/pull/34427
 if VERSION >= v"1.5.0-DEV.124"
@@ -54,6 +59,7 @@ export Bound,
        HB,
        first,
        last,
+       only,
        span,
        bounds_types,
        isclosed,

src/anchoredinterval.jl

@@ -176,23 +176,31 @@ span(interval::AnchoredInterval{P}) where P = abs(P)
 
 ##### CONVERSION #####
 
-# Allows an interval to be converted to a scalar when the set contained by the interval only
-# contains a single element.
+function only(interval::AnchoredInterval{P}) where {P}
+    if isclosed(interval) && (sign(P) == 0 || first(interval) == last(interval))
+        return first(interval)
+    else
+        throw(DomainError(interval, "The interval is not closed with coinciding endpoints"))
+    end
+end
+
+# Remove in version 2.0.0
 function Base.convert(::Type{T}, interval::AnchoredInterval{P,T}) where {P,T}
     if isclosed(interval) && (sign(P) == 0 || first(interval) == last(interval))
+        depwarn(
+            "`convert(::Type{T}, interval::AnchoredInterval{P,T})` is deprecated, " *
+            "use `only(interval::AnchoredInterval{P,T})` instead.",
+            :convert,
+        )
         return first(interval)
     else
-        # Remove deprecation in version 2.0.0
         depwarn(
-            "`convert(T, interval::AnchoredInterval{P,T})` is deprecated for " *
+            "`convert(::Type{T}, interval::AnchoredInterval{P,T})` is deprecated for " *
             "intervals which are not closed with coinciding endpoints. " *
             "Use `anchor(interval)` instead.",
             :convert,
         )
         return anchor(interval)
-
-        # TODO: For when deprecation is removed
-        # throw(DomainError(interval, "The interval is not closed with coinciding endpoints"))
     end
 end
 

src/interval.jl

@@ -235,18 +235,24 @@ end
 
 ##### CONVERSION #####
 
-# Allows an interval to be converted to a scalar when the set contained by the interval only
-# contains a single element.
-function Base.convert(::Type{T}, interval::Interval{T}) where T
+function only(interval::Interval)
     if first(interval) == last(interval) && isclosed(interval)
         return first(interval)
     else
         throw(DomainError(interval, "The interval is not closed with coinciding endpoints"))
     end
 end
 
-##### DISPLAY #####
+function Base.convert(::Type{T}, interval::Interval{T}) where {T}
+    depwarn(
+        "`convert(::Type{T}, interval::Interval{T})` is deprecated, " *
+        "use `only(interval)` instead.",
+        :convert,
+    )
+    return only(interval)
+end
 
+##### DISPLAY #####
 
 function Base.show(io::IO, interval::Interval{T,L,R}) where {T,L,R}
     if get(io, :compact, false)

test/anchoredinterval.jl

@@ -114,17 +114,16 @@ using Intervals: Bounded, Ending, Beginning, canonicalize, isunbounded
 
     @testset "conversion" begin
         interval = AnchoredInterval{Hour(0)}(dt)
-        @test convert(DateTime, interval) == dt
+        @test only(interval) == dt
 
         he = HourEnding(dt)
         hb = HourBeginning(dt)
 
-        # Note: When the deprecation is dropped remove the deprecated tests and uncomment
-        # the DomainError tests
+        @test_throws DomainError only(he)
+        @test_throws DomainError only(hb)
+
         @test (@test_deprecated convert(DateTime, he)) == anchor(he)
         @test (@test_deprecated convert(DateTime, hb)) == anchor(hb)
-        # @test_throws DomainError convert(DateTime, he)
-        # @test_throws DomainError convert(DateTime, hb)
 
         @test convert(Interval, he) == Interval{Open, Closed}(dt - Hour(1), dt)
         @test convert(Interval, hb) == Interval{Closed, Open}(dt, dt + Hour(1))

test/interval.jl

@@ -98,19 +98,22 @@
     end
 
     @testset "conversion" begin
-        @test_throws DomainError convert(Int, Interval{Open, Open}(10, 10))
-        @test_throws DomainError convert(Int, Interval{Open, Closed}(10, 10))
-        @test_throws DomainError convert(Int, Interval{Closed, Open}(10, 10))
-        @test convert(Int, Interval{Closed, Closed}(10, 10)) == 10
-        @test_throws DomainError convert(Int, Interval{Closed, Closed}(10, 11))
+        @test_throws DomainError only(Interval{Open, Open}(10, 10))
+        @test_throws DomainError only(Interval{Open, Closed}(10, 10))
+        @test_throws DomainError only(Interval{Closed, Open}(10, 10))
+        @test only(Interval{Closed, Closed}(10, 10)) == 10
+        @test_throws DomainError only(Interval{Closed, Closed}(10, 11))
+
+        @test (@test_deprecated convert(Int, Interval{Closed, Closed}(10, 10))) == 10
+        @test_throws DomainError (@test_deprecated convert(Int, Interval{Closed, Closed}(10, 11)))
 
         for T in (Date, DateTime)
             dt = T(2013, 2, 13)
-            @test_throws DomainError convert(T, Interval{Open, Open}(dt, dt))
-            @test_throws DomainError convert(T, Interval{Open, Closed}(dt, dt))
-            @test_throws DomainError convert(T, Interval{Closed, Open}(dt, dt))
-            @test convert(T, Interval{Closed, Closed}(dt, dt)) == dt
-            @test_throws DomainError convert(T, Interval{Closed, Closed}(dt, dt + Day(1)))
+            @test_throws DomainError only(Interval{Open, Open}(dt, dt))
+            @test_throws DomainError only(Interval{Open, Closed}(dt, dt))
+            @test_throws DomainError only(Interval{Closed, Open}(dt, dt))
+            @test only(Interval{Closed, Closed}(dt, dt)) == dt
+            @test_throws DomainError only(Interval{Closed, Closed}(dt, dt + Day(1)))
         end
     end