<h1 id="idempotency">Idempotency<a aria-hidden="true" class="anchor-heading icon-link" href="#idempotency"></a></h1>
In mathematics, the an idempotent function is one that will yield the same output, even as its output feeds back as input indefinitely, such as:
<code>Math.abs(Math.abs(Math.abs(Math.abs(-2))))</code>
<code>String( String( x ) )</code>
a way to test mathematical idempotency is to check if the output of a single function is equal to multiple calls of that function:
<pre class="language-js"><code class="language-js">currency( -3.1 ) == currency( currency( -3.1 ) )
// true
</code></pre>
Wherever possible, restricting side effects to idempotent operations is much better than unrestricted updates.
The programming-oriented definition for idempotence is similar, but less formal. Instead of requiring <code>f(x) === f(f(x))</code>, this view of idempotence is just that <code>f(x);</code> results in the same program behavior (in other words, not just the output. All impacts of the function) as <code>f(x);</code> <code>f(x);</code>. In other words, the result of calling <code>f(x)</code> subsequent times after the first call doesn't change anything.
<ul>
<li>Pure functions are idempotent in the programming sense</li>
</ul>
If you need to do side-effects, try to make it idempotent
Pure functions can reference <code>free variables</code> (ie. those that are not defined within the function scope), as long as those variables are sure to not change during the execution of the program (ie. they are constant)
An example of idempotency is in Postgres, when we say <code>delete function if exists</code>, rather than just <code>delete function</code>
<ul>
<li>It is idempotent because running the command more than once has no additional effect than simply running it once.</li>
</ul>
<hr>
Backlinks
<ul>
<li><a href="/notes/mn5VHtlB66IBGAFXPXgvq">HTTP Methods</a></li>
<li><a href="/notes/59dedd99-adb7-430f-a849-b303425e3209">Hooks</a></li>
</ul>

Idempotency

tech

This Dendron vault of tech knowledge is organized according to domains and their sub-domains, along with specific implementation of those domains.

For instance, Git itself is a domain. Sub-domains of Git would include topics like `commit`,
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The goal of the wiki is to present data in a manner that is from the perspective
of a querying user. Here, a user is a programmer wanting to get key information
from a specific domain. For instance, if a user wants to use postgres functions
and hasn't done them in a while, they should be able to query
`postgres.functions` to see basic implementations, as well as common patterns
that have been employed in the past.

This wiki has been written with myself in mind. While learning each of these
domains, I have been sensitive to the "aha" moments and have noted down my
insights as they arose. I have refrained from capturing information that I
considered obvious or otherwise non-beneficial to my own understanding.

As a result, I have allowed myself to use potentially arcane concepts to help
explain others. For example, in my note on [[unit testing|testing.method.unit]],
I have made reference to the [[microservices|general.arch.microservice]] note.
The ability to analogize between different concepts captured in different notes
allows an opportunity to build strong generalized understandings. Given that
you'd have to understand microservices to be able to draw that same parallel
that I've already drawn, these links won't work for everyone. Since these notes
are written for myself, I have been fine with taking these liberties and leaning
on them heavily.

What I hope to gain from this wiki is the ability to step away from any
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whatever my goals are within a short period of time. Of course this is all
vague sounding, and really depends on the domain along with the ends I am
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To achieve this, the system should be steadfast to:
- be able to put information in relatively easily, without too much thought
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This Dendron notebook is the sister vault to the general [Second Brain](https://tech.kyletycholiz.com).

## Tags
Throughout the garden, I have made use of tags, which give semantic meaning to the pieces of information.

- `ex.` - Denotes an *example* of the preceding piece of information
- `spec:` - Specifies that the preceding information has some degree of *speculation* to it, and may not be 100% factual. Ideally this gets clarified over time as my understanding develops. I try to go back after I have better understood the topic and clear out the notes of `spec:` tags
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- `mn:` - Denotes a *mnemonic*
- `expl:` - Denotes an *explanation*

## Resources
### UE (Unexamined) Resources
Often, I come across sources of information that I believe to be high-quality. They may be recommendations or found in some other way. No matter their origin, I may be in a position where I don't have the time to fully examine them (and properly extract notes), or I may not require the information at that moment in time. In cases like these, I will add reference to a section of the note called **UE Resources**. The idea is that in the future when I am ready to examine them, I have a list of resources that I can start with. This is an alternative strategy to compiling browser bookmarks, which I've found can quickly become untenable.

### E (Examined) Resources
Once a resource has been thoroughly examined and has been mined for notes, it will be moved from *UE Resources* to *E Resources*. This is to indicate that (in my own estimation), there is nothing more to be gained from the resource that is not already in the note.

### Resources
This heading is for inexhaustible resources. 
- A prime example would be a quality website that continually posts articles.  - Another example would be a tool, such as software that measures frequencies in a room to help acoustically treat it.
