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The crucial design choice is that you can't get a Doodad by just saying oh, I'm sure this is a Doodad, I will validate later. You have to parse the thing you've got to get a Doodad if that's what you meant, and the parsing can fail because maybe it isn't one.

    let almost_pi: Rational = "22/7".parse().unwrap();

Here the example is my realistic::Rational. The actual Pi isn't a Rational number so we can't represent it, but 22 divided by 7 is a pretty good approximation considering.

I agree that many languages don't provide a nice API for this, but what I don't see (and maybe you have examples) is languages which do provide a nice API but call it validate. To me that naming would make no sense, but if you've got examples I'll look at them.

by whalesalad3 hours ago|

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The point is parse and validate are interchangeable words for the most part. If you’re parsing something you expect to be an int, but it’s a float or the letter “a” is that not invalid? Is this assessment a form of validating expectations? The line between parsing and validating doesn’t exist.

by tialaramex52 minutes ago|

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But they plainly aren't interchangeable? Just asserting that it's true doesn't make it true.