Here are some random useful snippets for dealing with caches in Drupal 8, just because I keep having to dig them up from the API.

I'll try to add more here as I go.

Set an expiring cache item

\<span class="token package">Drupal</span><span class="token punctuation">:</span><span class="token punctuation">:</span><span class="token function">cache</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token operator">-</span><span class="token operator">&gt;</span><span class="token function">set</span><span class="token punctuation">(</span><span class="token single-quoted-string string">'cache_key'</span><span class="token punctuation">,</span> <span class="token single-quoted-string string">'cache_data'</span><span class="token punctuation">,</span> <span class="token variable">$expiration_timestamp</span><span class="token punctuation">)</span><span class="token punctuation">;</span>

Set a permanent cache item

\<span class="token package">Drupal</span><span class="token punctuation">:</span><span class="token punctuation">:</span><span class="token function">cache</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token operator">-</span><span class="token operator">&gt;</span><span class="token function">set</span><span class="token punctuation">(</span><span class="token single-quoted-string string">'cache_key'</span><span class="token punctuation">,</span> <span class="token single-quoted-string string">'cache_data'</span><span class="token punctuation">,</span> CacheBackendInterface<span class="token punctuation">:</span><span class="token punctuation">:</span><span class="token constant">CACHE_PERMANENT</span><span class="token punctuation">)</span><span class="token punctuation">;</span>

Set a permanent cache item with tags

\<span class="token package">Drupal</span><span class="token punctuation">:</span><span class="token punctuation">:</span><span class="token function">cache</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token operator">-</span><span class="token operator">&gt;</span><span class="token function">set</span><span class="token punctuation">(</span><span class="token single-quoted-string string">'cache_key'</span><span class="token punctuation">,</span> <span class="token single-quoted-string string">'cache_data'</span><span class="token punctuation">,</span> CacheBackendInterface<span class="token punctuation">:</span><span class="token punctuation">:</span><span class="token constant">CACHE_PERMANENT</span><span class="token punctuation">,</span> <span class="token keyword">array</span><span class="token punctuation">(</span><span class="token single-quoted-string string">'tag_one'</span><span class="token punctuation">,</span> <span class="token single-quoted-string string">'second_tag'</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>

Fetch an item from the cache

<span class="token variable">$cache</span> <span class="token operator">=</span> \<span class="token package">Drupal</span><span class="token punctuation">:</span><span class="token punctuation">:</span><span class="token function">cache</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token operator">-</span><span class="token operator">&gt;</span><span class="token function">get</span><span class="token punctuation">(</span><span class="token single-quoted-string string">'cache_key'</span><span class="token punctuation">)</span><span class="token punctuation">;</span><span class="token keyword">if</span> <span class="token punctuation">(</span><span class="token operator">!</span><span class="token function">empty</span><span class="token punctuation">(</span><span class="token variable">$cache</span><span class="token operator">-</span><span class="token operator">&gt;</span><span class="token property">data</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>  <span class="token comment">// Do something with $cache-&gt;data here.</span><span class="token punctuation">}</span>

(Note that in Drupal 8 you don't have to manually check to make sure the cache isn't expired, thanks to this issue)

Invalidate a cache item

\<span class="token package">Drupal</span><span class="token punctuation">:</span><span class="token punctuation">:</span><span class="token function">cache</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token operator">-</span><span class="token operator">&gt;</span><span class="token function">invalidate</span><span class="token punctuation">(</span><span class="token single-quoted-string string">'cache_key'</span><span class="token punctuation">)</span><span class="token punctuation">;</span>

Invalidate multiple cache items

\<span class="token package">Drupal</span><span class="token punctuation">:</span><span class="token punctuation">:</span><span class="token function">cache</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token operator">-</span><span class="token operator">&gt;</span><span class="token function">invalidateMultiple</span><span class="token punctuation">(</span><span class="token variable">$array_of_cache_ids</span><span class="token punctuation">)</span><span class="token punctuation">;</span>

Invalidate specific cache tags

This one allows you to pass in an array of cache tags to invalidate manually.

<span class="token keyword">use</span> <span class="token package">Drupal<span class="token punctuation">\</span>Core<span class="token punctuation">\</span>Cache<span class="token punctuation">\</span>Cache</span><span class="token punctuation">;</span>Cache<span class="token punctuation">:</span><span class="token punctuation">:</span><span class="token function">invalidateTags</span><span class="token punctuation">(</span><span class="token punctuation">[</span><span class="token single-quoted-string string">'config:block.block.YOURBLOCKID'</span><span class="token punctuation">,</span> <span class="token single-quoted-string string">'config:YOURMODULE.YOURCONFIG'</span><span class="token punctuation">,</span> <span class="token single-quoted-string string">'node:YOURNID'</span><span class="token punctuation">]</span><span class="token punctuation">)</span><span class="token punctuation">;</span>

Note that the invalidation functions also exist for deleting caches, by just replacing invalidate with delete.

Flush the entire site cache

This one is still the same as Drupal 7.

<span class="token function">drupal_flush_all_caches</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>

The end!