randstring: allow specifying chars to pick from (#22222)

base/docs/helpdb/Base.jl

@@ -766,24 +766,6 @@ julia> a
 """
 select!
 
-"""
-    randstring([rng,] len=8)
-
-Create a random ASCII string of length `len`, consisting of upper- and
-lower-case letters and the digits 0-9. The optional `rng` argument
-specifies a random number generator, see [Random Numbers](@ref).
-
-# Example
-
-```jldoctest
-julia> rng = MersenneTwister(1234);
-
-julia> randstring(rng, 4)
-"mbDd"
-```
-"""
-randstring
-
 """
     Float64(x [, mode::RoundingMode])
 

base/random.jl

@@ -1618,15 +1618,42 @@ end
 Base.show(io::IO, u::UUID) = write(io, Base.repr(u))
 
 # return a random string (often useful for temporary filenames/dirnames)
+
+"""
+    randstring([rng=GLOBAL_RNG], [chars], [len=8])
+
+Create a random string of length `len`, consisting of characters from
+`chars`, which defaults to the set of upper- and lower-case letters
+and the digits 0-9. The optional `rng` argument specifies a random
+number generator, see [Random Numbers](@ref).
+
+# Examples
+```jldoctest
+julia> srand(0); randstring()
+"c03rgKi1"
+
+julia> randstring(MersenneTwister(0), 'a':'z', 6)
+"wijzek"
+
+julia> randstring("ACGT")
+"TATCGGTC"
+```
+
+!!! note
+    `chars` can be any collection of characters, of type `Char` or
+    `UInt8` (more efficient), provided [`rand`](@ref) can randomly
+    pick characters from it.
+"""
+function randstring end
+
 let b = UInt8['0':'9';'A':'Z';'a':'z']
     global randstring
-    randstring(r::AbstractRNG, n::Int) = String(b[rand(r, 1:length(b), n)])
-    randstring(r::AbstractRNG) = randstring(r,8)
-    randstring(n::Int) = randstring(GLOBAL_RNG, n)
-    randstring() = randstring(GLOBAL_RNG)
+    randstring(r::AbstractRNG, chars=b, n::Integer=8) = String(rand(r, chars, n))
+    randstring(r::AbstractRNG, n::Integer) = randstring(r, b, n)
+    randstring(chars=b, n::Integer=8) = randstring(GLOBAL_RNG, chars, n)
+    randstring(n::Integer) = randstring(GLOBAL_RNG, b, n)
 end
 
-
 # Fill S (resized as needed) with a random subsequence of A, where
 # each element of A is included in S with independent probability p.
 # (Note that this is different from the problem of finding a random

test/random.jl

@@ -543,3 +543,23 @@ let r = MersenneTwister(0)
     @inferred Base.Random.reserve_1(r)
     @inferred Base.Random.reserve(r, 1)
 end
+
+# test randstring API
+let b = ['0':'9';'A':'Z';'a':'z']
+    for rng = [[], [MersenneTwister(0)]]
+        @test length(randstring(rng...)) == 8
+        @test length(randstring(rng..., 20)) == 20
+        @test issubset(randstring(rng...), b)
+        for c = ['a':'z', "qwèrtï", Set(Vector{UInt8}("gcat"))],
+                len = [8, 20]
+            s = len == 8 ? randstring(rng..., c) : randstring(rng..., c, len)
+            @test length(s) == len
+            if eltype(c) == Char
+                @test issubset(s, c)
+            else # UInt8
+                @test issubset(s, map(Char, c))
+            end
+        end
+    end
+    @test randstring(MersenneTwister(0)) == randstring(MersenneTwister(0), b)
+end