CODEWITHSUNDEEP
castingf#literals
cmeeren
cmeeren

Reputation: 4210

Why can't you add int and float literals in F#?

In F#, if you write 3 + 2.5 you get a syntax error. You have to write e.g. 3. + 2.5 to make it work, which can get annoying in math-heavy domains with many numeric literals.

Seeing as many other languages (e.g. C#) handle this just fine, is there a particular reason why F# doesn't implicitly convert int literals to float (which is a lossless conversion as far as I know) when performing arithmetic operations?

Upvotes: 2

Views: 487

Answers (2)

TheQuickBrownFox
TheQuickBrownFox

Reputation: 10624

It's true that int to float is "safe". However, the lack of implicit conversion between types in general is considered to be a good feature of F# by many, as others have mentioned.

F# has much more extensive type-inference than C#. The types that are inferred by usage can be passed all the way through a large codebase. Implicit conversion between numeric types could complicate that inference can make it harder to understand type errors and increase the maintenance burden of the compiler code itself. In fact, F# doesn't perform any implicit conversions defined in C#.

By eliminating unnecessary casts, implicit conversions can improve source code readability. However, because implicit conversions do not require programmers to explicitly cast from one type to the other, care must be taken to prevent unexpected results.

Again, this decreases convenience but reduces the chance of incorrect behaviour, which can be a much bigger inconvenience later on, or for someone else.

Basically, this approach trades some convenience for another convenience (not having to write type names everywhere) and some increased safety/explicitness. I personally think it's a good trade-off for F#.

Upvotes: 6

JosephStevens
JosephStevens

Reputation: 1706

F# is a functional first language, one of the core values in functional languages is being able to reason about your code. Which is a fancy way of saying it's easy to understand what your code and what it is doing. Now explicit operations mean that your code will be easier to reason about, don't believe me?

Here is some python code that takes a number, turns it into a string, then back into a number, guess what it returns:

float(str(0.47000000000000003))

Did you guess 0.47000000000000003? Sorry, it's actually 0.46999999999999997! There are all sorts of weirdness like that when converting from double to decimal to float! Best to pick a type and stick to it. Now constantly having to specify the type might seem annoying at first, but the value of never having to worry about what types your functions are using, vs the the types being sent in... god help you if a library chose types for you as well... well, let's just say you will appreciate the explicitness as time goes on ;)

Upvotes: 2

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