# Function with "memory"
**URL:** https://discourse.julialang.org/t/function-with-memory/3391
**Category:** General Usage
**Created:** [April 26, 2017, 7:20pm UTC](https://discourse.julialang.org/t/function-with-memory/3391 "2017-04-26T19:20:02Z")
**Posts on this page:** 6
**Page:** 1
### Author:  [@robertdj](https://discourse.julialang.org/u/robertdj)
#### Post date: [April 26, 2017, 7:20pm UTC](https://discourse.julialang.org/t/function-with-memory/3391/1 "2017-04-26T19:20:02Z")
I want to make a function with “memory”, that only modifies the second argument if the first satisfies certain conditions and otherwise returns the same second argument. Both arguments should be “scalar”/only one scalar value is of interest.
In the solution below `b` is **not** modified if `0 <= a <= 1`:
```julia
function foo(a, b)
if a < 0
b[1] = 1
elseif a > 1
b[1] = 0
end
b
end
b = [2]
foo(0.5, b)
foo(1.5, b)
foo(-0.5, b)
```
However, it seems clumsy to use a vector only to act as a container. Any good suggestions for a better solution?
---
### Author:  [@yuyichao](https://discourse.julialang.org/u/yuyichao)
#### Post date: [April 26, 2017, 7:26pm UTC](https://discourse.julialang.org/t/function-with-memory/3391/2 "2017-04-26T19:26:06Z")
It’s unclear what exactly do you want. If you just want a condition, you can just return the modified value. Or if you don’t want to use return value, you’ll have to use a mutable input type to get a “output” argument. You can use any mutable types for it including `Array`, `RefValue` or any custom types.
---
### Author:  [@robertdj](https://discourse.julialang.org/u/robertdj)
#### Post date: [April 26, 2017, 7:30pm UTC](https://discourse.julialang.org/t/function-with-memory/3391/3 "2017-04-26T19:30:20Z")
I’m not familiar with `RefValue` and no results turn up when searching in the docs – do you have a reference?
I actually thought that `Array`s where the only mutable (non-custom) type…?
---
### Author:  [@dpsanders](https://discourse.julialang.org/u/dpsanders)
#### Post date: [April 26, 2017, 7:34pm UTC](https://discourse.julialang.org/t/function-with-memory/3391/4 "2017-04-26T19:34:40Z")
Don’t think of “modifying” the argument, just return it:
```julia
function foo(a, b)
if a < 0
b = 1
elseif a > 1
b = 0
end
return b
end
a = 1; b = 2
b = foo(a, b)
```
---
### Author:  [@ChrisRackauckas](https://discourse.julialang.org/u/ChrisRackauckas)
#### Post date: [April 26, 2017, 7:36pm UTC](https://discourse.julialang.org/t/function-with-memory/3391/5 "2017-04-26T19:36:40Z")
There’s no performance gain with trying to do in-place updating of immutable types. Instead, there’s actually a performance loss. Purely using immutables is fastest, it’s just that in many cases this cannot be done (like in cases with array of arbitrary length).
---
### Author:  [@robertdj](https://discourse.julialang.org/u/robertdj)
#### Post date: [April 26, 2017, 7:39pm UTC](https://discourse.julialang.org/t/function-with-memory/3391/6 "2017-04-26T19:39:53Z")
That’s an excellent point – thanks!