writeAll
public func writeAll[W](mutating W, from: ArraySlice[UInt8]) -> Result[(), IoError] where W: Writable, W: not CopyableWrites every byte in buf, looping until the full slice has been
consumed. Returns .Err(brokenPipe()) if the writer reports 0 bytes
written before the slice is exhausted (matches Rust's
WriteAll/ErrorKind::WriteZero).
Examples
var file = try File.create("output.bin");
try writeAll(file, from: data.asSlice());Defined in lang/std/io/write.ks