# Handling Operating System Variation¶

When dealing with platform libraries, it is often necessary to provide special cases for various platforms. The variable Sys.KERNEL can be used to write these special cases. There are several functions intended to make this easier: is_unix, is_linux, is_apple, is_bsd, and is_windows. These may be used as follows:

if is_windows()
some_complicated_thing(a)
end


Note that is_linux and is_apple are mutually exclusive subsets of is_unix. Additionally, there is a macro @static which makes it possible to use these functions to conditionally hide invalid code, as demonstrated in the following examples.

Simple blocks:

ccall( (@static is_windows() ? :_fopen : :fopen), ...)


Complex blocks:

@static if is_linux()
some_complicated_thing(a)
else
some_different_thing(a)
end


When chaining conditionals (including if/elseif/end), the @static must be repeated for each level (parentheses optional, but recommended for readability):

@static is_windows() ? :a : (@static is_apple() ? :b : :c)