# Binary dollar sign operator

**URL:** <https://discourse.julialang.org/t/binary-dollar-sign-operator/123046>\
**Category:** General Usage\
**Tags:** question\
**Created:** [November 25, 2024, 1:47pm UTC](https://discourse.julialang.org/t/binary-dollar-sign-operator/123046 "2024-11-25T13:47:15Z")\
**Posts on this page:** 2\
**Page:** 1

<div class="post-metadata">

**Author:** ![phx](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/phx/32/219940_2.png) [@phx](https://discourse.julialang.org/u/phx)\
**Post date:** [November 25, 2024, 1:47pm UTC](https://discourse.julialang.org/t/binary-dollar-sign-operator/123046/1 "2024-11-25T13:47:15Z")

</div>

Hi everyone,  
I was reading an XML file describing a style for highlighting Julia syntax, when I noticed in the “operators” category the operators `$` and `$=`. I only know `$` for string interpolation, and that’s the only result I find for `$` if I search online. That’s also the only result the REPL returns if I search `$` in help mode:

```julia-repl
help?> $

  $

  Interpolation operator for interpolating into e.g. strings and expressions.

```

Interestingly, for `$=` I get

```julia-repl
help?> $=
search: >= = $ .= <= != ==

  x $= y is a synonym for x = x $ y

```

but what is this binary `$` operator exactly? I can’t find it in the documentation…

---

<div class="post-metadata">

**Author:** ![jakobjpeters](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/jakobjpeters/32/207797_2.png) [@jakobjpeters](https://discourse.julialang.org/u/jakobjpeters)\
**Post date:** [November 25, 2024, 1:52pm UTC](https://discourse.julialang.org/t/binary-dollar-sign-operator/123046/2 "2024-11-25T13:52:25Z")

</div>

I think the docstring is just indicating that the `$=` is syntactically available, even though it’s not yet defined as a function. For example:

```julia-repl
julia> ($)(x, y) = (x, y);

julia> x = 1;

julia> x $= 2
(1, 2)

```