Module: gears.cache

Cache object with data that can be garbage-collected.

Here is an example with a basic cache:

Usage example output:

new entry created with value 0
0
new entry created with value 1
42
new entry created with value 2
84
0

Usage:

  • local test_cache = cache.new(function(test)
        -- let's just print about what we created
        print('new entry created with value ' .. test)
        -- Pretend this is some expensive computation
        return test * 42
    end)
    -- Populate the cache
    print(test_cache:get(0))
    print(test_cache:get(1))
    print(test_cache:get(2))
    -- no message since it exists
    print(test_cache:get(0))
    
    The example below demonstrates how the garbage collector will clear the
    cache:
    
    
    
    
    *Usage example output**:
    
       cache object #0 for first
       cache object #1 for second
       cache object #0 for first
       forcing a garbage collect
       cache object #2 for first
       cache object #3 for second
    
    
  • local function tostring_for_cache(obj)
        return obj[1]
    end
    local counter = 0
    local wrapper_cache = gears.cache.new(function(arg)
        local kind = 'cache object #' .. tostring(counter) .. ' for ' .. tostring(arg)
        counter = counter + 1
        return setmetatable({ kind }, { __tostring = tostring_for_cache })
    end)
    print(wrapper_cache:get('first'))
    print(wrapper_cache:get('second'))
    -- No new object since it already exists
    print(wrapper_cache:get('first'))
    print('forcing a garbage collect')
    -- The GC can *always* clear the cache
    collectgarbage('collect')
    print(wrapper_cache:get('first'))
    print(wrapper_cache:get('second'))
    
    

Info:

  • Copyright: 2015 Uli Schlachter
  • Author: Uli Schlachter

Constructors

gears.cache (creation_cb) Create a new cache object.

Methods

:get (...) Get an entry from the cache, creating it if it’s missing.


Constructors

gears.cache (creation_cb)
Create a new cache object. A cache keeps some data that can be garbage-collected at any time, but might be useful to keep.

Parameters:

  • creation_cb Callback that is used for creating missing cache entries.

Returns:

    A new cache object.

Methods

:get (...)
Get an entry from the cache, creating it if it’s missing.

Parameters:

  • ... Arguments for the creation callback. These are checked against the cache contents for equality.

Returns:

    The entry from the cache
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