106 lines
3.6 KiB
ReStructuredText
106 lines
3.6 KiB
ReStructuredText
Nullable variable
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==========================
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.. objectives:: Objectives
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Now in this section we would like to make it possible that it is not necessary to specify a value
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for a variable.
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With rougail, it is possible for a variable's setttings have no value (nothing, null, None),
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that is, neither an assigned value nor a default value.
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.. prerequisites:: Prerequisites
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- We assume that Rougail's library is :ref:`installed <installation>` on your computer.
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- It is possible to retrieve the current state of the various Rougail files manipulated in this tutorial step
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by checking out the corresponding tag of the `rougail-tutorials` git repository.
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Each tag corresponds to a stage of progress in the tutorial.
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Of course, you can also decide to copy/paste or download the tutorial files contents while following the tutorial steps.
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If you want to follow this tutorial with the help of the corresponding :tutorial:`rougail-tutorials git repository <src/branch/1.1>`,
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this workshop page corresponds to the tags :tutorial:`v1.1_090 <src/tag/v1.1_090/README.md>` to :tutorial:`v1.1_091 <src/tag/v1.1_091/README.md>`
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in the repository.
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::
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git clone https://forge.cloud.silique.fr/stove/rougail-tutorials.git
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git switch --detach v1.1_090
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Variable with the value "null"
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------------------------------------
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.. note:: It is important to keep in mind that in Rougail a variable is :term:`mandatory` by default,
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meaning that it must either have a default value set or a :term:`user data` value assigned in the :term:`user data file`\ .
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This is Rougail's default behavior.
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Besides, note that the explicit keyword to express the setting "no value, nothing" in YAML is the `null` explicit keyword.
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Here is how we are going to specify a "no value" (nothing, `null`) as a possible setting for the `address` variable in the `socks_proxy` family.
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We need to:
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- explicitely disable the default :term:`mandatory` behavior (we will set it to `false`,
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- redefine the
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- define a default value of None (null).
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.. extinclude:: https://forge.cloud.silique.fr/stove/rougail-tutorials/raw/commit/v1.1_090/firefox/20-manual.yml
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:language: yaml
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:caption: The :file:`firefox/20-manual.yml` structure file with the `mandatory` set to `false` and the `null` (nothing) setting
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..
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%YAML 1.2
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---
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version: 1.1
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manual:
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use_for_https: true # Also use this proxy for HTTPS
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https_proxy:
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description: HTTPS Proxy
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type: proxy
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hidden:
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variable: _.use_for_https
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address:
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redefine: true
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description: HTTPS proxy address
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port:
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redefine: true
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description: HTTPS proxy port
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socks_proxy:
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description: SOCKS Proxy
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type: proxy
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address:
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redefine: true
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description: SOCKS proxy address
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default: null
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mandatory: false
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port:
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redefine: true
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description: SOCKS proxy port
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default: 1080
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version:
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description: SOCKS host version used by proxy
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choices:
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- v4
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- v5
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default: v5
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...
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Here are somme maybe usefull explanations:
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- Allowing the "no value, nothing" behavior is easy, we just add the `mandatory: false` attribute,
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- we explicitely need to set the `redefine: true` attribute because in the type `proxy` type setting
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we didn't set the `mandatory` attribute to false, this is then a type redefinition,
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- finally we can set the `default: null` that means that we can set no value to our address variable.
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