Initial value in minimum/maximum (#222)

Author: jishnub

src/cumsum.jl

@@ -72,16 +72,21 @@ function Base.issorted(a::RangeCumsum{<:Any,<:AbstractUnitRange{<:Integer}})
     length(r2) <= 1 + (last(r) >= 0)
 end
 
-function Base.minimum(a::RangeCumsum{<:Any, <:OneTo})
-    isempty(a) && throw(ArgumentError("RangeCumsum must be non-empty"))
+struct _InitialValue end
+
+_reduce_empty(init) = init
+_reduce_empty(::_InitialValue) = throw(ArgumentError("RangeCumsum must be non-empty"))
+
+function Base.minimum(a::RangeCumsum{<:Any, <:OneTo}; init = _InitialValue())
+    isempty(a) && return _reduce_empty(init)
     first(a)
 end
-function Base.maximum(a::RangeCumsum{<:Any, <:OneTo})
-    isempty(a) && throw(ArgumentError("RangeCumsum must be non-empty"))
+function Base.maximum(a::RangeCumsum{<:Any, <:OneTo}; init = _InitialValue())
+    isempty(a) && return _reduce_empty(init)
     last(a)
 end
-function Base.maximum(a::RangeCumsum{<:Any, <:AbstractUnitRange{<:Integer}})
-    isempty(a) && throw(ArgumentError("RangeCumsum must be non-empty"))
+function Base.maximum(a::RangeCumsum{<:Any, <:AbstractUnitRange{<:Integer}}; init = _InitialValue())
+    isempty(a) && return _reduce_empty(init)
     r = parent(a)
     if -first(r) in r
         r2 = r[searchsortedfirst(r, -first(r)+1):end]
@@ -90,8 +95,8 @@ function Base.maximum(a::RangeCumsum{<:Any, <:AbstractUnitRange{<:Integer}})
         max(first(r), sum(r))
     end
 end
-function Base.minimum(a::RangeCumsum{<:Any, <:AbstractUnitRange{<:Integer}})
-    isempty(a) && throw(ArgumentError("RangeCumsum must be non-empty"))
+function Base.minimum(a::RangeCumsum{<:Any, <:AbstractUnitRange{<:Integer}}; init = _InitialValue())
+    isempty(a) && return _reduce_empty(init)
     r = parent(a)
     if zero(eltype(r)) in r
         r2 = r[firstindex(r):searchsortedlast(r, zero(eltype(r)))]

test/test_cumsum.jl

@@ -107,13 +107,17 @@ cmpop(p) = isinteger(real(first(p))) && isinteger(real(step(p))) ? (==) : (≈)
         a = RangeCumsum(2:1)
         @test_throws ArgumentError minimum(a)
         @test_throws ArgumentError maximum(a)
+        @test minimum(a, init=10) == 10
+        @test maximum(a, init=0) == 0
 
         a = RangeCumsum(Base.OneTo(4))
         @test maximum(a) == 10
         @test minimum(a) == 1
         a = RangeCumsum(Base.OneTo(0))
         @test_throws ArgumentError minimum(a)
         @test_throws ArgumentError maximum(a)
+        @test minimum(a, init=10) == 10
+        @test maximum(a, init=0) == 0
 
         @testset "infinite" begin
             r = RangeCumsum(-5:ℵ₀)