Class: Alf::Types::TupleExpression

Inherits:
Object
  • Object
show all
Defined in:
lib/alf/types/tuple_expression.rb

Overview

A tuple expression is a Ruby expression whose evaluates in the scope of a specific tuple.

Example:

expr = TupleExpression["status * 10"]
expr.call(:status => 20)
# => 200

Instance Attribute Summary collapse

Class Method Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(expr, source = nil, result_type = Object) ⇒ TupleExpression

Creates a tuple expression from a Proc object

Parameters:

  • expr (Proc) —

    a Proc for the expression

  • source (String) (defaults to: nil) —

    the source code of the expression (optional)


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# File 'lib/alf/types/tuple_expression.rb', line 27

def initialize(expr, source = nil, result_type = Object)
  @expr_lambda = expr
  @source = source
  @result_type = result_type
end

Instance Attribute Details

#expr_lambda ⇒ Proc (readonly)

Returns the lambda expression.

Returns:

  • (Proc) —

    the lambda expression


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# File 'lib/alf/types/tuple_expression.rb', line 15

def expr_lambda
  @expr_lambda
end

#result_type ⇒ Class (readonly)

Returns the resulting type (Object by default).

Returns:

  • (Class) —

    the resulting type (Object by default)


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# File 'lib/alf/types/tuple_expression.rb', line 21

def result_type
  @result_type
end

#source ⇒ String (readonly)

Returns the expression source code (may be nil).

Returns:

  • (String) —

    the expression source code (may be nil)


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# File 'lib/alf/types/tuple_expression.rb', line 18

def source
  @source
end

Class Method Details

.coerce(arg) ⇒ TupleExpression Also known as: []

Coerces `arg` to a tuple expression.

Implemented coercions are:

  • TupleExpression -> self

  • Proc -> TupleExpression.new(arg, nil)

  • Symbol -> TupleExpression.new(…, arg)

Parameters:

  • arg (Object) —

    a value to convert to a tuple expression

Returns:

Raises:

  • (ArgumentError) —

    if the coercion fails


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# File 'lib/alf/types/tuple_expression.rb', line 45

def coerce(arg)
  case arg
  when TupleExpression
    arg
  when Proc
    TupleExpression.new(arg)
  when AttrName
    TupleExpression.new(eval("->(t){ t.#{arg} }"), "t.#{arg}")
  else
    raise ArgumentError, "Invalid argument `#{arg}` for TupleExpression()"
  end
end

Instance Method Details

#==(other) ⇒ Boolean Also known as: eql?

Checks equality with another expression

Parameters:

Returns:

  • (Boolean) —

    true if self and other are equal, false otherwise


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# File 'lib/alf/types/tuple_expression.rb', line 93

def ==(other)
  return false unless other.is_a?(TupleExpression)
  if source.nil? || other.source.nil?
    expr_lambda == other.expr_lambda
  else
    source == other.source
  end
end

#evaluate(scope = nil) ⇒ Object

Evaluates the expression in the context of a TupleScope

Parameters:

  • scope (TupleScope) (defaults to: nil) —

    a tuple scope instance.

Returns:

  • (Object) —

    the result of evaluating the expression in the context of `scope`


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# File 'lib/alf/types/tuple_expression.rb', line 66

def evaluate(scope = nil)
  result = if @expr_lambda.arity == 1
    @expr_lambda.call(scope)
  else
    scope.instance_exec(&@expr_lambda)
  end
  looks_an_expression?(result) ? result.to_relation : result
end

#has_source_code! ⇒ String

Asserts that this expression knows its source code or raises a NotImplementedError.

Returns:

  • (String) —

    the source code when known


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# File 'lib/alf/types/tuple_expression.rb', line 123

def has_source_code!
  if source.nil?
    raise NotImplementedError, "No known source code for this expression"
  else
    source
  end
end

#hash ⇒ Integer

Returns a hash code.

Returns:

  • (Integer) —

    a hash code for this expression


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# File 'lib/alf/types/tuple_expression.rb', line 85

def hash
  @source.nil? ? @expr_lambda.hash : @source.hash
end

#infer_type ⇒ Class

Infers the resulting type.

Returns:

  • (Class) —

    the type inferred from expression source code


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# File 'lib/alf/types/tuple_expression.rb', line 78

def infer_type
  result_type || Object
end

#to_lispy ⇒ String

Returns a lispy expression.

Returns:

  • (String) —

    a lispy expression for this tuple expression


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# File 'lib/alf/types/tuple_expression.rb', line 106

def to_lispy
  "->(t){ #{has_source_code!} }"
rescue NotImplementedError => ex
  "->(t){ [code unavailable] }"
end

#to_ruby_literal ⇒ String

Returns a ruby literal for this expression.

Returns:

  • (String) —

    a literal s.t. `eval(self.to_ruby_literal) == self`


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# File 'lib/alf/types/tuple_expression.rb', line 115

def to_ruby_literal
  "Alf::#{Support.class_name(self.class)}[#{Support.to_ruby_literal(has_source_code!)}]"
end