Define length methods for various iterators, using Inf as length for infinite iterators. See JuliaCollections/Iterators.jl#42

Author: simonbyrne

base/iterator.jl

@@ -120,6 +120,7 @@ countfrom(start::Number)               = Count(start, one(start))
 countfrom()                            = Count(1, 1)
 
 eltype{S}(it::Count{S}) = S
+length(it::Count) = Inf
 
 start(it::Count) = it.start
 next(it::Count, state) = (state, state + it.step)
@@ -134,6 +135,7 @@ end
 take(xs, n::Int) = Take(xs, n)
 
 eltype(it::Take) = eltype(it.xs)
+length(it::Take) = min(length(it.xs), n)
 
 start(it::Take) = (it.n, start(it.xs))
 
@@ -157,6 +159,7 @@ end
 drop(xs, n::Int) = Drop(xs, n)
 
 eltype(it::Drop) = eltype(it.xs)
+length(it::Drop) = max(length(it.xs)-n, 0)
 
 function start(it::Drop)
     xs_state = start(it.xs)
@@ -181,6 +184,7 @@ end
 cycle(xs) = Cycle(xs)
 
 eltype(it::Cycle) = eltype(it.xs)
+length(it::Cycle) = Inf
 
 function start(it::Cycle)
     s = start(it.xs)
@@ -205,6 +209,8 @@ immutable Repeated{O}
 end
 repeated(x) = Repeated(x)
 eltype{O}(r::Repeated{O}) = O
+length(x::Repeated) = Inf
+
 start(it::Repeated) = nothing
 next(it::Repeated, state) = (it.x, nothing)
 done(it::Repeated, state) = false

test/functional.jl

@@ -48,6 +48,7 @@ let b = IOBuffer("1\n2\n3\n"), a = []
         push!(a, (i,x))
     end
     @test a == [(1,"1\n"),(2,"2\n"),(3,"3\n")]
+    @test length(enumerate(eachline(b))) == 3
 end
 
 # zip eachline (issue #7369)
@@ -58,6 +59,10 @@ let zeb     = IOBuffer("1\n2\n3\n4\n5\n"),
         push!(res, (parse(Int,strip(number)), letter))
     end
     @test res == [(1, 'a'), (2, 'b'), (3, 'c'), (4, 'd'), (5, 'e')]
+    @test length(zip(eachline(zeb), letters)) == 5
+    @test length(zip(eachline(zeb), 1:10)) == 5
+    @test length(zip(eachline(zeb), countfrom(1))) == 5
+    @test length(zip(eachline(zeb), 1:3)) == 3
 end
 
 # rest
@@ -67,6 +72,8 @@ let s = "hello"
     @test collect(rest(s, st)) == ['e','l','l','o']
 end
 
+
+
 # countfrom
 # ---------
 
@@ -77,6 +84,8 @@ let i = 0
         i <= 10 || break
     end
 end
+@test length(countfrom(0,2)) == Inf
+@test length(countfrom(0)) == Inf
 
 # take
 # ----
@@ -99,6 +108,10 @@ let i = 0
     @test i == 10
 end
 
+@test length(take(1:10,5)) == 5
+@test length(take(1:10,15)) == 10
+@test length(take(countfrom(1),5)) == 5
+
 # drop
 # ----
 
@@ -110,6 +123,11 @@ let i = 0
     @test i == 4
 end
 
+@test length(drop(1:10,5)) == 5
+@test length(drop(1:10,15)) == 0
+@test length(drop(countfrom(0),5)) == Inf
+
+
 # cycle
 # -----
 
@@ -121,6 +139,8 @@ let i = 0
     end
 end
 
+@test length(cycle(0:3)) == Inf
+
 # repeated
 # --------
 
@@ -138,3 +158,6 @@ let i = 0
         i <= 10 || break
     end
 end
+
+@test length(repeated(1)) == Inf
+@test length(repeated(1,10)) == 10