terminology – What does the term Fallback mean?

Question:

I've seen this term fallback used several times. Even in the framework I use every day, Laravel 5, this word appears in a certain configuration:

Example:

/*
|--------------------------------------------------------------------------
| Application Locale Configuration
|--------------------------------------------------------------------------
|
| The application locale determines the default locale that will be used
| by the translation service provider. You are free to set this value
| to any of the locales which will be supported by the application.
|
*/

'locale' => 'pt_br',

/*
|--------------------------------------------------------------------------
| Application Fallback Locale
|--------------------------------------------------------------------------
|
| The fallback locale determines the locale to use when the current one
| is not available. You may change the value to correspond to any of
| the language folders that are provided through your application.
|
*/

'fallback_locale' => 'en',

From what I can understand in the example above, this fallback word is more or less in the sense of: "use this location if the other one is not available" .

This is what I could understand simply by analyzing it, but I searched the internet around the world and came to the conclusion that the term could be more comprehensive.

So, I would like to know:

  • What does the term fallback mean in our "programming world"? Is it a default value if another fails, or does it go beyond that?

  • Is this word related to rollback ?

Answer:

According to Wikipedia it is a contingency option, meaning something is used when its original option is not available for some reason.

This is a generic definition that serves computing well. Of course, in each context it can have a more specific meaning, but it always has this basis. And it is used in very different contexts (infrastructure in general, project management, software development, configurations, algorithms, data structures, tests, specific technologies, etc.), some are even in technology specifications.

The translation is just contingency or plan B.

There's not much secret, rules, nothing. It's just having an option chosen automatically when the main one isn't present or available for some reason. Note that the unavailability can be momentary or even selected by some specific criteria according to the wishes of the person who made the software, probably following some requirements.

This is different from having a default option where you have something chosen and only if another is explicitly chosen does it change the option. The fallback occurs automatically and the noun is the opposite of default , which is not the default.

Examples

An example is a runtime environment that tries to use a native option, not having it available it tries to emulate the execution (rendering something, compilation, etc.).

There are cases where the term can be used for backup options, such as a database that springs into action when another fails, but this usage is less common, and often the term used is backup .

There is a lot of talk about fallback when using web technologies where a mechanism may not be available in a browser. It even hasmarkings to indicate the contingency .

But it can be extended to any technology. It is used when multiple versions are available and one of them is preferred, but others can do as well.

Nor will I mention examples of hardware, networks, etc. because that's not our focus, but it's where it happens very often to give it more reliability.

Rollback

The only relationship is that the two end with a back . This term is the action of going back, undoing what was done and returning to the original state. Usually because of a glitch, but it might just be by choice.

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