Add append!/push!/pushfirst!/pop!/popfirst! for BlockVector

[tkf]

This PR adds append!, push!, pushfirst!, pop!, and popfirst! for BlockVector.

It also adds foldl (and reduce because why not) for BlockVector since it is essential for fast iteration (see #116 (comment) below).

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It's not the main point of this PR but a few quick benchmarks for foldl and reduce alone (just to help justify their inclusion):

Before:

julia> @btime sum($(mortar([rand(100) for _ in 1:10])));
  13.494 μs (0 allocations: 0 bytes)

julia> @btime foldl(+, $(mortar([rand(100) for _ in 1:10])));
  13.637 μs (0 allocations: 0 bytes)

After:

julia> @btime sum($(mortar([rand(100) for _ in 1:10])));
  130.989 ns (0 allocations: 0 bytes)

julia> @btime foldl(+, $(mortar([rand(100) for _ in 1:10])));
  1.090 μs (3 allocations: 80 bytes)

[tkf]

Using foldl is faster when src is a block vector.

With this PR:

julia> @btime append!(x, $(mortar([rand(3) for _ in 1:100]))) setup=(x = mortar([[0.0]]));
  912.130 ns (5 allocations: 9.29 KiB)

With this PR but using for loop:

julia> @btime append!(x, $(mortar([rand(3) for _ in 1:100]))) setup=(x = mortar([[0.0]]));
  11.031 μs (7 allocations: 2.58 KiB)

[dlfivefifty]

This adds a new block right? I would call this blockappend!, and add a blockpop!, etc.

[tkf]

Renamed it and added a docstring. Please check if the behavior I described is OK.

It actually does not always add a single block. If src is a block vector, it can add multiple blocks.

(Also, I haven't added blockpop! etc. yet.)

[dlfivefifty]

Add tests (here and below) that make clear the resulting block structure. That is (I think):

@test dest[Block(1)]  == [1,2,3]
@test dest[Block(2)]  == [4,5,6]

[tkf]

I added a few tests for the block structure. Actually, @test dest[Block(2)] == [4,5,6] is not always true. Let me know if the block structure makes sense.

[dlfivefifty]

I think the block structure should be consistent, that is, append!(::AbstractBlockVector, ::AbstractVector) should either always add to the last block or add new blocks.

There's a question here what append!(::AbstractBlockVector, ::AbstractBlockVector) should do...

[tkf]

So, to make things predictable, maybe you'd like something like

append!(dest, src): always mutate the last block (blocklength(dest) is constant)

blockappend!(dest, src): always add blocklength(src) blocks and avoid copy when make sense

?

[dlfivefifty]

Yes that's reasonable.

[codecov]

Codecov Report

Merging #116 into master will increase coverage by 0.67%.
The diff coverage is 91.66%.

@@            Coverage Diff             @@
##           master     #116      +/-   ##
==========================================
+ Coverage   84.42%   85.09%   +0.67%     
==========================================
  Files          12       14       +2     
  Lines         822      906      +84     
==========================================
+ Hits          694      771      +77     
- Misses        128      135       +7     

Impacted Files	Coverage Δ
src/BlockArrays.jl	100.00% <ø> (ø)
src/blockdeque.jl	91.13% <91.13%> (ø)
src/blockreduce.jl	100.00% <100.00%> (ø)

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[tkf]

OK, I think I addressed the comments.