# When and How to use Types

**URL:** <https://discourse.julialang.org/t/when-and-how-to-use-types/56659>\
**Category:** General Usage\
**Tags:** question, performance, parametric-types\
**Created:** [March 7, 2021, 7:33am UTC](https://discourse.julialang.org/t/when-and-how-to-use-types/56659 "2021-03-07T07:33:03Z")\
**Posts on this page:** 1\
**Showing post:** 2

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**Author:** ![mkitti](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/mkitti/32/12459_2.png) [@mkitti](https://discourse.julialang.org/u/mkitti)\
**Post date:** [March 7, 2021, 8:09am UTC](https://discourse.julialang.org/t/when-and-how-to-use-types/56659/2 "2021-03-07T08:09:43Z")

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Interpolations.jl is written the way it is such that you can obtain a specialized type that takes advantage of multiple dispatch for subsequent operations.

In terms of type stability, you want to get a consistent output type for a set of input types. Sometimes this means encoding some values as types. For a quick way to do so, see [`Val`](https://docs.julialang.org/en/v1/manual/types/#%22Value-types%22).

I suggest that you use tools like `@code_warntype`, `@code_lowered`, `@code_llvm`, and `@code_native` to explore what the compiler is doing.

Let’s take a simple example:

```julia
julia> f(x) = 5 + 5
f (generic function with 1 method)

julia> @code_lowered f(1)
CodeInfo(
1 ─ %1 = 5 + 5
└── return %1
)

julia> @code_llvm f(1)

; @ REPL[125]:1 within `f'
; Function Attrs: uwtable
define i64 @julia_f_3722(i64) #0 {
top:
  ret i64 10
}

julia> @code_native f(1)
        .text
; ┌ @ REPL[125]:1 within `f'
        pushq %rbp
        movq %rsp, %rbp
        movl $10, %eax
        popq %rbp
        retq
        nopl (%rax,%rax)
; └

```

Above we see that LLVM has figured out that it can precompute `5 + 5` and the assembly shows that the function just returns `10`. It does not add `5 + 5` every time.

`!` is used for negation. The only unary operators are listed here:  
[https://github.com/JuliaLang/julia/blob/master/src/julia-parser.scm#L99-L100](https://github.com/JuliaLang/julia/blob/master/src/julia-parser.scm#L99-L100)

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