Fuzion • Idioms • Idiom # 95: Get file size

Idiom # 95: Get file size

Code

The variable x in this case will be of type outcome i64, i.e., it will be either the file size or an instance of error in case the file size could not be determined. A match expression is needed to extract the size.

Alternatively, the following code forcefully extracts the size from the result, but will crash in case of an error:

Running Example

ex95 is

  path := "idiom95.testfile"

  # create the file
  o0 := io.file.use unit path io.file.mode.write ()->
    _ := io.file.writer.write "hello".utf8
  handle_error o0

  # size without error handling, will set x to choice type `outcome i64`
  x0 := (io.file.stat path true).bind i64 x->x.size
  say "the size of $path is $x0"

  # size without error handling, will fail at precondition or panic in case of an error
  x1 := (io.file.stat path true).val.size
  say "the size of $path is $x1"

  # size with manual error handling
  match io.file.stat path true
    d io.file.meta_data => x := d.size                   # logic in case of success
                           say "the size of $path is $x"
    e error             => say e                         # error handling

  # delete the file
  o1 := io.file.delete path
  handle_error o1

  handle_error (e outcome T) =>
    if e!!
      panic $e.err

What are effects?

last changed: 2025-05-13

next: Idiom # 96: Check string prefix