# When is it necessary to qualify names

**URL:** <https://discourse.julialang.org/t/when-is-it-necessary-to-qualify-names/25378>\
**Category:** New to Julia\
**Tags:** question, faq\
**Created:** [June 17, 2019, 8:42pm UTC](https://discourse.julialang.org/t/when-is-it-necessary-to-qualify-names/25378 "2019-06-17T20:42:52Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![Ross\_Boylan](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/ross_boylan/32/9210_2.png) [@Ross\_Boylan](https://discourse.julialang.org/u/Ross_Boylan)\
**Post date:** [June 17, 2019, 8:42pm UTC](https://discourse.julialang.org/t/when-is-it-necessary-to-qualify-names/25378/1 "2019-06-17T20:42:52Z")

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I am having trouble figuring out when I need to qualify names or `use` modules and when I don’t.

1. `*` seems to do matrix multiplication even though I haven’t even issued `using LinearAlgebra`.
2. `optimize` worked after `using Optim` but I needed `Optim.minimizer` to get that value out of the result. Admittedly the latter was in a slightly different environment, namely a juno session with namespace set to the module in which Optim was used.
3. I needed `Iterators.product` to use `product`. I did this even though I had no `using Iterators` directive. And I also did not need `Base.Iterators.product`, which I gather is the full name.

My understanding is that in principle I can use exported names unqualified after `using` the module that exports them, and other names in the module with qualification. But the documentation I’ve looked at doesn’t seem to flag the distinction when discussing different functions.

More hazily, I think `Base` and some other modules are always available (unless I take special steps) and so I can access its members easily. This may explain why `Iterators` rather than `Base.Iterators` is sufficient.

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**Author:** ![JeffreySarnoff](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/jeffreysarnoff/32/1980_2.png) [@JeffreySarnoff](https://discourse.julialang.org/u/JeffreySarnoff)\
**Post date:** [June 18, 2019, 2:20am UTC](https://discourse.julialang.org/t/when-is-it-necessary-to-qualify-names/25378/2 "2019-06-18T02:20:18Z")

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This is a very good question; one that should benefit many. Thank you for asking.

When Julia starts interactively, one sees the prompt `julia >` … many functions are available immediately just by typing their names. How many? Which functions? [click on this to see that](https://github.com/JuliaLang/julia/blob/master/base/exports.jl)

Many more functions and organized capabilities are available and at hand for use.  
Here starts the use of qualified names. `Base` itself has submodules. The submodules contain functions. To use one of those functions, use the submodule name to qualify the function name. [click on this link to see the submodules](https://docs.julialang.org/en/v1.2-dev/base/base/#Base-Submodules-1)

Next are functions from members of the standard library. To use these, you have to _use_ them like this: `using LinearAlgebra`. They are in the docs, from [Base64](https://docs.julialang.org/en/v1.2-dev/stdlib/Base64/) to [Unicode](https://docs.julialang.org/en/v1.2-dev/stdlib/Unicode/), includINT: `Pkg`, `Dates`, `Statistics`, `LinearAlgebra`, `Random`.

Beyond that are the packages of our ecosystem.

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<div class="post-metadata">

**Author:** ![c42f](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/c42f/32/52842_2.png) [@c42f](https://discourse.julialang.org/u/c42f)\
**Post date:** [June 18, 2019, 3:38am UTC](https://discourse.julialang.org/t/when-is-it-necessary-to-qualify-names/25378/3 "2019-06-18T03:38:33Z")

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> [@Ross\_Boylan](#):
>
> `*` seems to do matrix multiplication even though I haven’t even issued `using LinearAlgebra` .

Yes. When you type `using A`, two quite distinct things happen:

- The code from `A` is _loaded_ into the runtime. This may add new methods to existing functions.
- The export list from `A` is made available as names (bindings) in the current module.

Because the function `*` comes from Base you already have access to that name, so the name import part of `using LinearAlgebra` is irrelevant to whether `*` can multiply matrices. Instead, it depends on whether the code from `LinearAlgebra` is loaded. In the default setup this code is _always_ loaded because `LinearAlgebra` is a standard library.