RequestStore#fetch without &block

&block in method definitions creates additional proc which consumes more time and memory.

One of the usecase of RequestStore is to memoize value on per request basis. Currently, in this scenario while using RequestStore#fetch unused proc will be created multiple times


Benchmark:

2.4.3 :001 > require 'memory_profiler'
 => true
2.4.3 :002 > require 'request_store'
 => true
2.4.3 :003 > require 'benchmark/ips'
 => true
2.4.3 :004 >
2.4.3 :005 >   module RequestStore
2.4.3 :006?>     def self.fetch_without_proc_creation(key)
2.4.3 :007?>         # Suggested
2.4.3 :008 >           store[key] = yield unless exist?(key)
2.4.3 :009?>         store[key]
2.4.3 :010?>       end
2.4.3 :011?>     def self.fetch_with_proc_creation(key, &block)
2.4.3 :012?>         # current
2.4.3 :013 >           store[key] = yield unless exist?(key)
2.4.3 :014?>         store[key]
2.4.3 :015?>       end
2.4.3 :016?>   end ; nil
 => nil
2.4.3 :017 >
2.4.3 :018 >   Benchmark.ips do |x|
2.4.3 :019 >       x.config(:time => 5, :warmup => 2)
2.4.3 :020?>     x.report("with &block") { RequestStore.fetch_with_proc_creation(:a){0} }
2.4.3 :021?>
2.4.3 :022 >       x.report("without &block") {RequestStore.fetch_without_proc_creation(:b){1}}
2.4.3 :023?>
2.4.3 :024 >       x.compare!
2.4.3 :025?>   end ; nil
Warming up --------------------------------------
         with &block   101.397k i/100ms
      without &block   157.885k i/100ms
Calculating -------------------------------------
         with &block      1.474M (± 2.6%) i/s -      7.402M in   5.024766s
      without &block      2.554M (± 1.9%) i/s -     12.789M in   5.009695s

Comparison:
      without &block:  2553852.9 i/s
         with &block:  1474212.3 i/s - 1.73x  slower

 => nil
2.4.3 :026 >
2.4.3 :027 >   MemoryProfiler.report{ 100.times{ RequestStore.fetch_with_proc_creation(:aa){0} } }.pretty_print(detailed_report: false, allocated_strings: false, retained_strings: 0)
Total allocated: 8000 bytes (100 objects)
Total retained:  0 bytes (0 objects)

Allocated String Report
-----------------------------------

 => nil
2.4.3 :028 >
2.4.3 :029 >   MemoryProfiler.report{ 100.times{ RequestStore.fetch_without_proc_creation(:bb){1} } }.pretty_print(detailed_report: false, allocated_strings: false, retained_strings: 0)
Total allocated: 0 bytes (0 objects)
Total retained:  0 bytes (0 objects)

Allocated String Report
-----------------------------------

 => nil
2.4.3 :030 >

lib/request_store.rb

@@ -43,7 +43,7 @@ def self.exist?(key)
     store.key?(key)
   end
 
-  def self.fetch(key, &block)
+  def self.fetch(key)
     store[key] = yield unless exist?(key)
     store[key]
   end