add efficient findfirst method for StepRange (#30778)

JuliaLang · Jan 23, 2019 · 91162e9 · 91162e9
1 parent 81ef652
commit 91162e9
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diff --git a/base/array.jl b/base/array.jl
@@ -1741,6 +1741,13 @@ end
 findfirst(testf::Function, A::Union{AbstractArray, AbstractString}) =
  findnext(testf, A, first(keys(A)))
 
+function findfirst(p::Union{Fix2{typeof(isequal),T},Fix2{typeof(==),T}}, r::StepRange{T,S}) where {T,S}
+ first(r) <= p.x <= last(r) || return nothing
+ d = convert(S, p.x - first(r))
+ iszero(d % step(r)) || return nothing
+ return d ÷ step(r) + 1
+end
+
 """
  findprev(A, i)
 

diff --git a/test/ranges.jl b/test/ranges.jl
@@ -269,6 +269,12 @@ end
  @test findall(in(span), r) == 1:6
  end
  end
+ @testset "findfirst" begin
+ @test findfirst(isequal(7), 1:2:10) == 4
+ @test findfirst(==(7), 1:2:10) == 4
+ @test findfirst(==(10), 1:2:10) == nothing
+ @test findfirst(==(11), 1:2:10) == nothing
+ end
  @testset "reverse" begin
  @test reverse(reverse(1:10)) == 1:10
  @test reverse(reverse(typemin(Int):typemax(Int))) == typemin(Int):typemax(Int)