# Confusing difference: ^literal vs ^variable

**URL:** <https://discourse.julialang.org/t/confusing-difference-literal-vs-variable/13515>\
**Category:** General Usage\
**Created:** [August 15, 2018, 5:26pm UTC](https://discourse.julialang.org/t/confusing-difference-literal-vs-variable/13515 "2018-08-15T17:26:47Z")\
**Posts on this page:** 1\
**Showing post:** 6

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**Author:** ![StefanKarpinski](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/stefankarpinski/32/24_2.png) [@StefanKarpinski](https://discourse.julialang.org/u/StefanKarpinski)\
**Post date:** [August 16, 2018, 8:32am UTC](https://discourse.julialang.org/t/confusing-difference-literal-vs-variable/13515/6 "2018-08-16T08:32:59Z")

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This was a controversial change and there are still many people who are not entirely comfortable with it. The starting point is that people do not really often expect or want `x^2` and `x^-1` to be `pow(x, 2)` and `pow(x, -1)`, respectively. Rather, people want `x^2` to be syntax for `x*x` and `x^-1` to be a syntax for `1/x`. These can both generally be implemented much more efficiently than calling a general power function—but in completely different ways. With sufficiently clever optimizations (constant propagation + power reduction), one can potentailly optimize `pow(x, 2)` into `x*x` but it would be even better if we didn’t have to do such a clever optimization in the first place. It’s been a fairly common and successful strategy in the design of Julia to arrange things so that you can get great performance in a straightforward way without need for clever optimizations instead of trying to make the optimizers smarter. So what this design does is it causes `x^n` where `n` is a _literal_ integer value to call `Base.literal_pow(x, Val(n))`, which allows us to specialize the syntax on individual literal values like 2 or -1. This allow us to make `x^2` actually mean `x*x` instead of needing to try to optimize it to that. It also allows us to make negative literal exponents work without introducing a type instability in the general `^` function. And indeed, we used to get regular complaints from new users that `2^-1` doesn’t return `0.5` as they would expect, instead giving them a domain error because of the negative exponent. There are good reasons for it but users don’t care about involved language design reasons, they just want it to work. A way to think about this is that `^2` is its own operator, as is `^3` and `^-1`, and so on. Hopefully that helps.

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_[View the full topic](https://discourse.julialang.org/t/confusing-difference-literal-vs-variable/13515)._