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Comment by QuercusMax | Hacker News Reader

Was the expect method supposed to be named except, as in exception? That would make a lot more sense.

If I recall correctly we just couldn't come up with a great name for it. To me "expect" is a positive action, but the argument is about it failing to meet the expectation. Semantically I like `thing.unwrap_or(|| panic!("failure message"))`. It feels more like what I would want to say, but it just is so wordy.

Ultimately I'm happy we just picked something and moved on, but still mildly annoys me whenever I write it. If only we found that perfect method name way back when...

The java optional api uses orElseThrow which I think is quite clear.

Agreed, I've never liked 'expect' either; 'or_else_panic(msg)' would be much clearer

Edit: 'or_panic(msg)' would be shorter and also good.

I think that was one of the proposed variations, but we ended up picking the shorter .expect to cut down on repetition. We expected (ha) that this function would be used in these one-offs, so we wanted something more efficient.

As an old Java hack, my allowance for repetition is high. Especially when using and IDE that basically writes the code for me ;)

otherwise(msg)?

I would expect such a function to provide a default value

I actually initially had it as sort of a callback:

.otherwise(panic(msg))

(although I assume a rust panic! isn't really a function call).

But isn't the way to get the default, simply to use unwrap()?

In a simple script, failing to open a configuration file for reading is likely a show stopper, and you probably want to log/print an error (no such file, wrong permission, etc).

But in, say, a paint program, you'd normally not want to panic and crash if the image file a user selected to open in a file dialog is invalid or went away between the click-to-select and the click-to-open. In such a program you'd want to handle most file errors much more defensively.

It is, but also quite long, which I do not think suits Rust naming conventions.

Not really though: 'unwrap_or_else' is of similar length.

  .beware("could not open file");

    .be_wary_of("but hole")

Not a Rust guy, but it looks like a way to say "this option value is required and if it is not present, crash with the following error". So "expect" is a fair name, since it means a value is expected and the absence of a value is unexpected.

I could see "required" or "require" as a better name. Or even just break the "positive names" rule and go with "notOptional".

Looking at it that way, I think it's possible to make "expect" more comfortable to read by how you phrase your error messages.

Instead of

    let mut file = File::open("conf.json")
        .expect("could not open file");

and

    let config: Value = serde::from_reader(file)
        .expect("config has invalid json");

and

    let jenkins_server = config.get("jenkins_server")
        .expect("jenkins_server key not in config")
        .as_str()
        .expect("jenkins_server key is not a string");

One could write

    let mut file = File::open("conf.json")
        .expect("Need to be able to open file `conf.json'.");

and

    let config: Value = serde::from_reader(file)
        .expect("The file `conf.json' must contain valid JSON.");

and

    let jenkins_server = config.get("jenkins_server")
        .expect("The config must have a key named `jenkins_server'.")
        .as_str()
        .expect("The config value of `jenkins_server' must be a string.");

Something like that.

That is a good point. I'm going to have to start being more positive in my expectations :)

I think it's like Assert. You pass an error message the same way you pass an error message to assert.

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