Misc fixes

Project.toml

@@ -1,6 +1,6 @@
 name = "MemoryViews"
 uuid = "a791c907-b98b-4e44-8f4d-e4c2362c6b2f"
-version = "0.3.0"
+version = "0.3.1"
 authors = ["Jakob Nybo Nissen <jakobnybonissen@gmail.com>"]
 
 [weakdeps]

src/basic.jl

@@ -44,9 +44,11 @@ function Base.getindex(v::MemoryView, i::Integer)
 end
 
 function Base.similar(::MemoryView{T1, M}, ::Type{T2}, dims::Tuple{Int}) where {T1, T2, M}
-    len = Int(only(dims))::Int
+    len = only(dims)
     memory = Memory{T2}(undef, len)
-    MemoryView{T2, M}(unsafe, memoryref(memory), len)
+    # Note: `similar` needs to construct a mutable memory view, even if the input
+    # type is not mutable
+    MemoryView(memory)
 end
 
 function Base.empty(::MemoryView{T1, M}, ::Type{T2}) where {T1, T2, M}
@@ -101,6 +103,8 @@ end
 Base.getindex(v::MemoryView, ::Colon) = v
 Base.@propagate_inbounds Base.view(v::MemoryView, idx::AbstractUnitRange) = v[idx]
 
+# Efficient way to get `mem[1:include_last]`.
+# include_last must be in 0:length(mem)
 function truncate(mem::MemoryView, include_last::Integer)
     lst = Int(include_last)::Int
     @boundscheck if (lst % UInt) > length(mem) % UInt
@@ -109,6 +113,8 @@ function truncate(mem::MemoryView, include_last::Integer)
     typeof(mem)(unsafe, mem.ref, lst)
 end
 
+# Efficient way to get `mem[from:end]`.
+# From must be in 1:length(mem).
 function truncate_start_nonempty(mem::MemoryView, from::Integer)
     frm = Int(from)::Int
     @boundscheck if ((frm - 1) % UInt) ≥ length(mem) % UInt
@@ -118,11 +124,14 @@ function truncate_start_nonempty(mem::MemoryView, from::Integer)
     typeof(mem)(unsafe, newref, length(mem) - frm + 1)
 end
 
+# Efficient way to get `mem[from:end]`.
+# From must be in 1:length(mem)+1.
 function truncate_start(mem::MemoryView, from::Integer)
     frm = Int(from)::Int
     @boundscheck if ((frm - 1) % UInt) > length(mem) % UInt
         throw(BoundsError(mem, frm))
     end
+    frm == 1 && return mem
     newref = @inbounds memoryref(mem.ref, frm - (from == length(mem) + 1))
     typeof(mem)(unsafe, newref, length(mem) - frm + 1)
 end
@@ -320,12 +329,16 @@ function Base.reverse!(mem::MutableMemoryView)
 end
 
 function Base.reverse(mem::MemoryView)
-    cp = MutableMemoryView(unsafe, copy(mem))
+    cp = similar(mem)
     stop = length(cp) + 1
     @inbounds for i in 1:length(cp)
         cp[i] = mem[stop - i]
     end
-    cp
+    return if mem isa MutableMemoryView
+        cp
+    else
+        ImmutableMemoryView(cp)
+    end
 end
 
 struct ReverseMemoryView{T}

test/runtests.jl

@@ -327,7 +327,7 @@ end
         mem = MemoryView("abc")
         mem2 = similar(mem)
         @test length(mem2) == length(mem)
-        @test typeof(mem2) == typeof(mem)
+        @test typeof(mem2) == MutableMemoryView{UInt8}
 
         mem = MemoryView(String["", "", ""])
         mem2 = similar(mem, Int, 4)
@@ -388,10 +388,15 @@ end
             @test reverse!(MemoryView(copy(v))) == MemoryView(reverse(v))
             mem = MemoryView(v)
             rev = reverse(mem)
+            @test typeof(rev) == typeof(mem)
             @test rev.ref != mem.ref
             @test rev == reverse(v)
             @test_throws Exception reverse!(ImmutableMemoryView(v))
         end
+        mem = MemoryView("abcd")
+        rev = reverse(mem)
+        @test rev == b"dcba"
+        @test rev isa ImmutableMemoryView{UInt8}
     end
 
     @testset "Cmp" begin
@@ -434,6 +439,12 @@ end
             @test_throws BoundsError split_first(mem)
             @test_throws BoundsError split_last(mem)
         end
+
+        # Split empty mem at
+        mem = MemoryView(UInt16[])
+        (v1, v2) = split_at(mem, 1)
+        @test v1 == v2
+        @test isempty(v1)
     end
 
     @testset "Split unaligned" begin