CODEWITHSUNDEEP
ocamlocaml-core
hugomg
hugomg

Reputation: 69924

Why does Core.Std deprecate the `close_in` and `close_out` functions?

If I open Core.Std, trying to use close_out function to close an out_channelgives me an error because Core changes the type signature of close_out to give me a deprecation error message.

close_out;;
- : [ `Deprecated_use_out_channel ] -> [ `Deprecated_use_out_channel ] = <fun>

First question: Why does Core deprecate close_out deprecated but not close_out_noerr?

Second question: Does Core still expect me to work with in_channels and out_channels or does it prefer that I use a different API for IO?

Third question: The only other IO API I could find are functions like read or write in the Unix module, which work on file descriptors instead of file handles. In C, the file descriptor functions emit syscalls directly while the ones from stdio.h that receive FILE * do buffered IO. Is this similar in Ocaml with the functions in Unix module emitting syscalls directly and the functions working with in_channel and out_channel do buffered IO?

Upvotes: 2

Views: 716

Answers (2)

Anthony Scemama
Anthony Scemama

Reputation: 1593

If you look at the Real World Ocaml book, the author seems to make extensive use of the In_channel and Out_channel modules. Files are no more opened/closed using the Ocaml pervasive functions but with the In_channel.close and Out_channel.close functions.

The problem is that if an exception is raised when reading the file, the programmer has to close the opened file when the exception is caught. There is no equivalent of garbage collector for opened files. Using In_channel.with_file takes care of proper file closing, even if an exception is raised.

Upvotes: 3

ivg
ivg

Reputation: 35210

The basic IO is implemeted in Out_channel and In_channel modules, that defines new interface for the old out_channel and in_channel types. Since the types are the same it is a thin overlay that interoperates smoothly with any other libraries.

What concerning close_out_noerr, it looks like that they just missed it. In genral, you should forget about OCaml Standard Library when using Core, and use only facilities provided by the latter. If you really need old standard library you can use Caml module.

Upvotes: 3

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