Let’s create 2 arrays first:

```
julia> a = rand(100); b = rand(100)
```

Take `identity(a)`

as an example. These works:

`identity(a) .= b`

`identity(a) .+= b`

`@. $identity(a) += b`

`x = identity(a); @. x = b`

But this doesn’t:

```
julia> @. $identity(a) = b
ERROR: syntax: invalid function name "$identity" around REPL[69]:1
```

Seems that Julia thinks I’m defining a function called `$identity`

.