# Do I need to specify concrete type of a variable such as Int64 or just Int, Float64 or just Float?

**URL:** <https://discourse.julialang.org/t/do-i-need-to-specify-concrete-type-of-a-variable-such-as-int64-or-just-int-float64-or-just-float/66047>\
**Category:** General Usage\
**Created:** [August 8, 2021, 9:53pm UTC](https://discourse.julialang.org/t/do-i-need-to-specify-concrete-type-of-a-variable-such-as-int64-or-just-int-float64-or-just-float/66047 "2021-08-08T21:53:04Z")\
**Posts on this page:** 1\
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**Author:** ![Sukera](https://avatars.discourse-cdn.com/v4/letter/s/ce7236/32.png) [@Sukera](https://discourse.julialang.org/u/Sukera)\
**Post date:** [August 9, 2021, 12:47am UTC](https://discourse.julialang.org/t/do-i-need-to-specify-concrete-type-of-a-variable-such-as-int64-or-just-int-float64-or-just-float/66047/5 "2021-08-09T00:47:56Z")

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> [@CRquantum](#):
>
> Is there performance difference?

Almost never, and almost certainly not in the cases you’re thinking of.

> [@CRquantum](#):
>
> Or, like, is it just using Int and Float is enough, and no need to particular do Int64 and Float64?

On 32 bit platforms, `Int` refers to `Int32`. On 64 bit platforms, `Int` refers to `Int64`. There is no equivalent shorthand for floating point numbers.

* * *

For variables, type assertions limit the type of that binding in the current scope to the asserted type.

For function arguments in function definitions, type assertions restrict the allowed incoming types for that argument.

For struct fields, type assertions signify that the field in question holds a value of the asserted type. The default constructors will try to convert incoming arguments to the types in question.

For more information, see the [section on type declarations in the docs](https://docs.julialang.org/en/v1/manual/types/#Type-Declarations).

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