Why do we need to prefix module name with Julia function sometimes to make it work?

General Usage
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1

As example, here is a DateTime object declared below using Dates module:

julia> using Dates

julia> dt = DateTime(2021, 05, 11, 18, 21, 50)
2021-05-11T18:21:50

We can find the Hour value of dt simply using hour() function from Dates module:

julia> hour(dt)
18

We can prefix the module name with hour() function also:

julia> Dates.hour(dt)
18

Now, if we try to use format() function from Dates module as below:

julia> format(dt, "e, H:M:S dd-u-yyyy")
ERROR: UndefVarError: format not defined

it throws error. We need to prefix module name here to make it work:

julia> Dates.format(dt, "e, H:M:S dd-u-yyyy")
"Tue, 18:21:50 11-May-2021"

Why do some functions in Julia need to be prefixed by the module name to work?

2

using Dates brings only the functions and types which were labeled with export inside the Dates module. For more about export and using, see: Modules · The Julia Language

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