# ArgTools

## Argument Handling

ArgTools.ArgReadType
ArgRead = Union{AbstractString, AbstractCmd, IO}

The ArgRead types is a union of the types that the arg_read function knows how to convert into readable IO handles. See arg_read for details.

ArgTools.ArgWriteType
ArgWrite = Union{AbstractString, AbstractCmd, IO}

The ArgWrite types is a union of the types that the arg_write function knows how to convert into writeable IO handles, except for Nothing which arg_write handles by generating a temporary file. See arg_write for details.

ArgTools.arg_readFunction
arg_read(f::Function, arg::ArgRead) -> f(arg_io)

The arg_read function accepts an argument arg that can be any of these:

• AbstractString: a file path to be opened for reading
• AbstractCmd: a command to be run, reading from its standard output
• IO: an open IO handle to be read from

Whether the body returns normally or throws an error, a path which is opened will be closed before returning from arg_read and an IO handle will be flushed but not closed before returning from arg_read.

Note: when opening a file, ArgTools will pass lock = false to the file open(...) call. Therefore, the object returned by this function should not be used from multiple threads. This restriction may be relaxed in the future, which would not break any working code.

ArgTools.arg_writeFunction
arg_write(f::Function, arg::ArgWrite) -> arg
arg_write(f::Function, arg::Nothing) -> tempname()

The arg_read function accepts an argument arg that can be any of these:

• AbstractString: a file path to be opened for writing
• AbstractCmd: a command to be run, writing to its standard input
• IO: an open IO handle to be written to
• Nothing: a temporary path should be written to

If the body returns normally, a path that is opened will be closed upon completion; an IO handle argument is left open but flushed before return. If the argument is nothing then a temporary path is opened for writing and closed open completion and the path is returned from arg_write. In all other cases, arg itself is returned. This is a useful pattern since you can consistently return whatever was written, whether an argument was passed or not.

If there is an error during the evaluation of the body, a path that is opened by arg_write for writing will be deleted, whether it's passed in as a string or a temporary path generated when arg is nothing.

Note: when opening a file, ArgTools will pass lock = false to the file open(...) call. Therefore, the object returned by this function should not be used from multiple threads. This restriction may be relaxed in the future, which would not break any working code.

ArgTools.arg_isdirFunction
arg_isdir(f::Function, arg::AbstractString) -> f(arg)

The arg_isdir function takes arg which must be the path to an existing directory (an error is raised otherwise) and passes that path to f finally returning the result of f(arg). This is definitely the least useful tool offered by ArgTools and mostly exists for symmetry with arg_mkdir and to give consistent error messages.

ArgTools.arg_mkdirFunction
arg_mkdir(f::Function, arg::AbstractString) -> arg
arg_mkdir(f::Function, arg::Nothing) -> mktempdir()

The arg_mkdir function takes arg which must either be one of:

• a path to an already existing empty directory,
• a non-existent path which can be created as a directory, or
• nothing in which case a temporary directory is created.

In all cases the path to the directory is returned. If an error occurs during f(arg), the directory is returned to its original state: if it already existed but was empty, it will be emptied; if it did not exist it will be deleted.

## Function Testing

ArgTools.arg_readersFunction
arg_readers(arg :: AbstractString, [ type = ArgRead ]) do arg::Function
## pre-test setup ##
@arg_test arg begin
## test using arg ##
end
## post-test cleanup ##
end

The arg_readers function takes a path to be read and a single-argument do block, which is invoked once for each test reader type that arg_read can handle. If the optional type argument is given then the do block is only invoked for readers that produce arguments of that type.

The arg passed to the do block is not the argument value itself, because some of test argument types need to be initialized and finalized for each test case. Consider an open file handle argument: once you've used it for one test, you can't use it again; you need to close it and open the file again for the next test. This function arg can be converted into an ArgRead instance using @arg_test arg begin ... end.

ArgTools.arg_writersFunction
arg_writers([ type = ArgWrite ]) do path::String, arg::Function
## pre-test setup ##
@arg_test arg begin
arg :: ArgWrite
## test using arg ##
end
## post-test cleanup ##
end

The arg_writers function takes a do block, which is invoked once for each test writer type that arg_write can handle with a temporary (non-existent) path and arg which can be converted into various writable argument types which write to path. If the optional type argument is given then the do block is only invoked for writers that produce arguments of that type.

The arg passed to the do block is not the argument value itself, because some of test argument types need to be initialized and finalized for each test case. Consider an open file handle argument: once you've used it for one test, you can't use it again; you need to close it and open the file again for the next test. This function arg can be converted into an ArgWrite instance using @arg_test arg begin ... end.

There is also an arg_writers method that takes a path name like arg_readers:

arg_writers(path::AbstractString, [ type = ArgWrite ]) do arg::Function
## pre-test setup ##
@arg_test arg begin
# here arg :: ArgWrite
## test using arg ##
end
## post-test cleanup ##
end

This method is useful if you need to specify path instead of using path name generated by tempname(). Since path is passed from outside of arg_writers, the path is not an argument to the do block in this form.

ArgTools.@arg_testMacro
@arg_test arg1 arg2 ... body

The @arg_test macro is used to convert arg functions provided by arg_readers and arg_writers into actual argument values. When you write @arg_test arg body it is equivalent to arg(arg -> body).