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Comment by dannymi | Hacker News Reader

I can see the value of a lint (if there's a newline without a comma, warn), but concatenating strings by multiplication is the correct thing to do (since it's also used this way in mathematics of parsers).

Using the plus operator to concatenate strings is just weird.

Think of the usual algebraic properties these operators are supposed to have.

"+" always is supposed to be commutative--so "a"+"b" = "b"+"a", if those mean alternatives (they usually do mean that in mathematics), is just fine.

On the other hand, multiplication is often not commutative--also not here. "a" "b" != "b" "a".

So string concatenation should be the latter. And indeed that's how it's in regular expression mathematics for example.

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Juxtaposition is not multiplication in this context - you can't write (2 3), for example, it has to be (2 * 3).

Furthermore, Python already uses * for strings to indicate repetition: ("foo" * 2 == "foofoo").

String concatenation really just needs its own separate operator. & is an obvious candidate, if only it wasn't so commonly appropriated for bitwise AND - which is a very poor use of a single-char operator as it's not something that you need often, especially in a language like Python.

On the other hand, D uses binary ~ for concatenation. That has a neat mnemonic: it's a "rope" that "ties strings together".

& is also used for set intersection in Python. I think + for string concatenation isn't too bad, really. It fits in with the fact that length(s + t) = length(s) + length(t), the same way we write A × B for Cartesian product (since |A × B| = |A| × |B|, even though this operation is neither commutative nor associative) or B^A for a function space (since |B^A| = |B|^|A|).

Which invertible commutative string operation would you choose for + ?

This might be nice from a math point of view, but I think users are going to be confused using "string"^3 for repetitions (instead of "string"*3). + and * make too much sense to the unwashed masses.

At any rate, explicit is better than implicit.

There is no reason you couldn't use str * str for concatenation and str * integer (or even string * real) repetition.

Well, except if you wanted to support user classes that could duck type as both strings and numbers, which it would make awkward.

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