3 ms·

The defer keyword seems pretty cool. I assume it creates a stack of calls to execute just before exiting scope. Personally I find it a cool little syntactic su

by deevus 12y ago

The defer keyword seems pretty cool. I assume it creates a stack of calls to execute just before exiting scope. Personally I find it a cool little syntactic sugar.

gnuvince 12y ago
Go has the same functionality, you should check it out. It's great, but I feel it's a "halfway solution": you open your file and then immediately add a `defer f.Close()` statement afterward, so you don't forget to close it in all exit paths of the function (i.e. early returns in branches), however you still need to remember to type the defer.
- ufo 12y ago
  In functional languages you often see functions like with_file that use a closure to denote the file lifetime: with_file(fun file -> use_file(file) ) I wonder if there is a way to code something similar that works with "defer". This would free you from needing to "remember" to add the defer and would have the advantage of allowing you to use `return` and `break` statements which don't work if you wrap them inside an inner function. The only thing I can think of is Python's with statement. Since its language syntax it allows for `return` and `break` but I wonder if there is a way to play nice with defer instead of requiring you to use another "block level" syntax construct for every file you use.
  - bjz_ 12y ago
    We used to do this in Rust, but have found RAII much better for this. Dealing with multiple resources open at once can quickly become painful. See http://blog.skylight.io/rust-means-never-having-to-close-a-socket/#facilitiesinotherlanguages http://blog.skylight.io/rust-means-never-having-to-close-a-s...
  - Too 12y ago
    Sounds like the finally-keyword in most languages?
- bjz_ 12y ago
  He does actually mention Go as the inspiration. Anyway, I still much prefer RAII for this - not only for guarding against your own forgetfulness, but also to make sure a rogue refactor or patch doesn't break anything.

by deevus 12y ago

The defer keyword seems pretty cool. I assume it creates a stack of calls to execute just before exiting scope. Personally I find it a cool little syntactic sugar.

gnuvince 12y ago

Go has the same functionality, you should check it out. It's great, but I feel it's a "halfway solution": you open your file and then immediately add a `defer f.Close()` statement afterward, so you don't forget to close it in all exit paths of the function (i.e. early returns in branches), however you still need to remember to type the defer.

ufo 12y ago
In functional languages you often see functions like with_file that use a closure to denote the file lifetime: with_file(fun file -> use_file(file) ) I wonder if there is a way to code something similar that works with "defer". This would free you from needing to "remember" to add the defer and would have the advantage of allowing you to use `return` and `break` statements which don't work if you wrap them inside an inner function. The only thing I can think of is Python's with statement. Since its language syntax it allows for `return` and `break` but I wonder if there is a way to play nice with defer instead of requiring you to use another "block level" syntax construct for every file you use.
- bjz_ 12y ago
  We used to do this in Rust, but have found RAII much better for this. Dealing with multiple resources open at once can quickly become painful. See http://blog.skylight.io/rust-means-never-having-to-close-a-socket/#facilitiesinotherlanguages http://blog.skylight.io/rust-means-never-having-to-close-a-s...
- Too 12y ago
  Sounds like the finally-keyword in most languages?
bjz_ 12y ago
He does actually mention Go as the inspiration. Anyway, I still much prefer RAII for this - not only for guarding against your own forgetfulness, but also to make sure a rogue refactor or patch doesn't break anything.