Small Array

wontruefree · July 16, 2021, 7:54pm

I am looking to make a SmallArray which is like StaticArray but more mutable. It will have size and grow but not reallocate memory. It seems like StaticArray is special in the say the compiler treats it.

adding a buffer

github.com

crystal-lang/crystal/blob/master/src/compiler/crystal/program.cr#L182-L185

    
      
          types["StaticArray"] = static_array = @static_array = StaticArrayType.new self, self, "StaticArray", value, ["T", "N"]
          static_array.struct = true
          static_array.declare_instance_var("@buffer", static_array.type_parameter("T"))
          static_array.can_be_stored = false

setup types and capacity

github.com

crystal-lang/crystal/blob/master/src/compiler/crystal/types.cr#L2181-L2213

    
      
          class StaticArrayType < GenericClassType
            def new_generic_instance(program, generic_type, type_vars)
              n = type_vars["N"]
          
          
    unless n.is_a?(Var) && n.type.is_a?(TypeParameter)
                unless n.is_a?(NumberLiteral)
                  raise TypeException.new "can't instantiate StaticArray(T, N) with N = #{n.type} (N must be an integer)"
                end
          
          
      value = n.value.to_i
                if value < 0
                  raise TypeException.new "can't instantiate StaticArray(T, N) with N = #{value} (N must be positive)"
                end
              end
          
          
    StaticArrayInstanceType.new program, generic_type, program.struct, type_vars
            end
          end
          
          
# An instantiated static array type, like StaticArray(UInt8, 256)

This file has been truncated. show original

Is there a way to have a struct and setup a buffer on the stack to store elements in for a SmallArray type container.

Blacksmoke16 · July 16, 2021, 8:10pm

If you know the size that the array will end up being, is there a reason to not just do like Array(Int32).new 123? This would set the internal capacity to store 123 items. It ofc wouldn’t prevent it from allocating more if you add more elements than was expected. But that may be okay depending on your exact use case?

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Small Array

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