count(regex, string) computes length(findall(regex, string)) better

NEWS.md

@@ -32,6 +32,7 @@ New library functions
 * `findfirst`, `findlast`, `findnext` and `findprev` now accept a character as first argument
   to search for that character in a string passed as the second argument ([#31664]).
 * New `findall(pattern, string)` method where `pattern` is a string or regex ([#31834]).
+* `count(pattern, string)` gives the number of things `findall` would match ([#32849]).
 * `istaskfailed` is now documented and exported, like its siblings `istaskdone` and `istaskstarted` ([#32300]).
 * `RefArray` and `RefValue` objects now accept index `CartesianIndex()` in  `getindex` and `setindex!` ([#32653])
 

base/regex.jl

@@ -328,26 +328,58 @@ findfirst(r::Regex, s::AbstractString) = findnext(r,s,firstindex(s))
 
 
 """
-    findall(pattern::Union{AbstractString,Regex}, string::AbstractString; overlap::Bool=false)
+    findall(
+        pattern::Union{AbstractString,Regex},
+        string::AbstractString;
+        overlap::Bool = false,
+    )
 
 Return a `Vector{UnitRange{Int}}` of all the matches for `pattern` in `string`.
 Each element of the returned vector is a range of indices where the
 matching sequence is found, like the return value of [`findnext`](@ref).
 
 If `overlap=true`, the matching sequences are allowed to overlap indices in the
-original string, otherwise they must be from distinct character ranges.
+original string, otherwise they must be from disjoint character ranges.
 """
 function findall(t::Union{AbstractString,Regex}, s::AbstractString; overlap::Bool=false)
     found = UnitRange{Int}[]
     i, e = firstindex(s), lastindex(s)
     while true
         r = findnext(t, s, i)
-        isnothing(r) && return found
+        isnothing(r) && break
         push!(found, r)
         j = overlap || isempty(r) ? first(r) : last(r)
-        j > e && return found
+        j > e && break
+        @inbounds i = nextind(s, j)
+    end
+    return found
+end
+
+"""
+    count(
+        pattern::Union{AbstractString,Regex},
+        string::AbstractString;
+        overlap::Bool = false,
+    )
+
+Return the number of matches for `pattern` in `string`. This is equivalent to
+calling `length(findall(pattern, string))` but more efficient.
+
+If `overlap=true`, the matching sequences are allowed to overlap indices in the
+original string, otherwise they must be from disjoint character ranges.
+"""
+function count(t::Union{AbstractString,Regex}, s::AbstractString; overlap::Bool=false)
+    n = 0
+    i, e = firstindex(s), lastindex(s)
+    while true
+        r = findnext(t, s, i)
+        isnothing(r) && break
+        n += 1
+        j = overlap || isempty(r) ? first(r) : last(r)
+        j > e && break
         @inbounds i = nextind(s, j)
     end
+    return n
 end
 
 """

test/regex.jl

@@ -46,12 +46,18 @@
     @test_throws ArgumentError match(r"test", GenericString("this is a test"))
     @test_throws ArgumentError findfirst(r"test", GenericString("this is a test"))
 
-    # findall:
+    # findall
     @test findall(r"\w+", "foo bar") == [1:3, 5:7]
     @test findall(r"\w+", "foo bar", overlap=true) == [1:3, 2:3, 3:3, 5:7, 6:7, 7:7]
     @test findall(r"\w*", "foo bar") == [1:3, 4:3, 5:7, 8:7]
     @test findall(r"\b", "foo bar") == [1:0, 4:3, 5:4, 8:7]
 
+    # count
+    @test count(r"\w+", "foo bar") == 2
+    @test count(r"\w+", "foo bar", overlap=true) == 6
+    @test count(r"\w*", "foo bar") == 4
+    @test count(r"\b", "foo bar") == 4
+
     # Named subpatterns
     let m = match(r"(?<a>.)(.)(?<b>.)", "xyz")
         @test (m[:a], m[2], m["b"]) == ("x", "y", "z")