# "inline" variable in closure

**URL:** <https://discourse.julialang.org/t/inline-variable-in-closure/93213>\
**Category:** General Usage\
**Tags:** closure\
**Created:** [January 19, 2023, 2:05pm UTC](https://discourse.julialang.org/t/inline-variable-in-closure/93213 "2023-01-19T14:05:24Z")\
**Posts on this page:** 3\
**Page:** 1

<div class="post-metadata">

**Author:** ![OvidiusCicero](https://avatars.discourse-cdn.com/v4/letter/o/73ab20/32.png) [@OvidiusCicero](https://discourse.julialang.org/u/OvidiusCicero)\
**Post date:** [January 19, 2023, 2:05pm UTC](https://discourse.julialang.org/t/inline-variable-in-closure/93213/1 "2023-01-19T14:05:24Z")

</div>

I have a some function depending on an independent variable and some general parameters. In a simplified version

```julia
f(a, x) = a + x

```

where `a` is some complicated struct of parameters which I ideally would like to type only once. from a type stability stand point this is perfectly fine:

```julia
@code_warntype f(1.0, 1.0)
MethodInstance for f(::Float64, ::Float64)
  from f(a, x) in Main at REPL[3]:1
Arguments
  #self#::Core.Const(f)
  a::Float64
  x::Float64
Body::Float64
1 ─ %1 = (a + x)::Float64
└── return %1

```

However, I need to shove this function into another function which only accepts one parameter [In this case it’s `nlsolve` from `NLsolve but I don’t think this is very relevant]. The usual way in another programming language would be to make a another closure like this:

```julia
a = 1
g(x) = f(a, x)

```

which is however not type stable and slow as shown by the `Any` in the return type:

```julia
@code_warntype g(1.0)
MethodInstance for g(::Float64)
  from g(x) in Main at REPL[5]:1
Arguments
  #self#::Core.Const(g)
  x::Float64
Body::Any
1 ─ %1 = Main.f(Main.a, x)::Any
└── return %1

```

If I do

```julia
h(x) = 1.0 + x

```

I again something type stable

```julia
@code_warntype h(1.0)
MethodInstance for h(::Float64)
  from h(x) in Main at REPL[7]:1
Arguments
  #self#::Core.Const(h)
  x::Float64
Body::Float64
1 ─ %1 = (1.0 + x)::Float64
└── return %1

```

How can I define a `g(x)` that lowers to the same code as `h(x)` but ideally without spelling the literal value of `a` in its body?

---

<div class="post-metadata">

**Author:** ![stevengj](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/stevengj/32/71_2.png) [@stevengj](https://discourse.julialang.org/u/stevengj)\
**Post date:** [January 19, 2023, 2:21pm UTC](https://discourse.julialang.org/t/inline-variable-in-closure/93213/2 "2023-01-19T14:21:14Z")

</div>

> [@OvidiusCicero](#):
>
> How can I define a `g(x)` that lowers to the same code as `h(x)` but ideally without spelling the literal value of `a` in its body?

[Write the code inside a function](https://docs.julialang.org/en/v1/manual/performance-tips/#Performance-critical-code-should-be-inside-a-function). The problem with `g(x) = f(a, x)` is simply that [`a` is a (non-`const`) global](https://docs.julialang.org/en/v1/manual/performance-tips/#Avoid-untyped-global-variables). e.g.

```julia
function foo(a)
    g(x) = f(a, x)
    # ... do something with g ... 
end

```

Instead of a function, you can also use a `let` block, e.g.

```julia
let a=1
    g(x) = f(a,x)
    # ... do something with g ...
end

```

but functions are more flexible, and in general it’s best to get out of the habit of writing your code in the form of scripts full of global variables.

---

<div class="post-metadata">

**Author:** ![OvidiusCicero](https://avatars.discourse-cdn.com/v4/letter/o/73ab20/32.png) [@OvidiusCicero](https://discourse.julialang.org/u/OvidiusCicero)\
**Post date:** [January 19, 2023, 2:22pm UTC](https://discourse.julialang.org/t/inline-variable-in-closure/93213/3 "2023-01-19T14:22:25Z")

</div>

thank you!