support open do ... end syntax

Author: bicycle1885

docs/src/index.md

@@ -51,26 +51,46 @@ The following snippet is an example of using CodecZlib.jl, which exports
 `TranscodingStream{GzipDecompression,S} where S<:IO`:
 ```julia
 using CodecZlib
-stream = GzipDecompressionStream(open("data.gzip"))
+stream = GzipDecompressionStream(open("data.txt.gz"))
 for line in eachline(stream)
     # do something...
 end
 close(stream)
 ```
 
+Note that the last `close` call will close the file as well.  Alternatively,
+`open(<stream type>, <filepath>) do ... end` syntax will close the file at the
+end:
+```julia
+using CodecZlib
+open(GzipDecompressionStream, "data.txt.gz") do stream
+    for line in eachline(stream)
+        # do something...
+    end
+end
+```
+
 ### Save a data matrix with Zstd compression
 
 Writing compressed data is easy. One thing you need to keep in mind is to call
 `close` after writing data; otherwise, the output file will be incomplete:
 ```julia
 using CodecZstd
-mat = randn(100, 100).^2
-file = open("data.mat.zst", "w")
-stream = ZstdCompressionStream(file)
+mat = randn(100, 100)
+stream = ZstdCompressionStream(open("data.mat.zst", "w"))
 writedlm(stream, mat)
 close(stream)
 ```
 
+Of course, `open(<stream type>, ...) do ... end` works well:
+```julia
+using CodecZstd
+mat = randn(100, 100)
+open(ZstdCompressionStream, "data.mat.zst", "w") do stream
+    writedlm(stream, mat)
+end
+```
+
 ### Explicitly finish transcoding by writing `TOKEN_END`
 
 When writing data, the end of a data stream is indicated by calling `close`,

src/stream.jl

@@ -75,6 +75,17 @@ end
 # Base IO Functions
 # -----------------
 
+function Base.open(f::Function, ::Type{T}, args...) where T<:TranscodingStream
+    try
+        stream = T(open(args...))
+        f(stream)
+    catch
+        rethrow()
+    finally
+        close(stream)
+    end
+end
+
 function Base.isopen(stream::TranscodingStream)
     return stream.state.state != :close
 end