class Chem::Metadata

• Chem::Metadata
• Reference
• Object

Overview

A Metadata is a hash-like container that holds metadata about an object. It maps a property name (as string) to a primitive value (integer, float, string, or bool) or an array of them. Most of the functionality mirrors that of a Hash, where some specific methods like Hash#dig or default values are excluded.

Values are stored as Any instances, which a thin wrapper for a dynamically-typed primitive value and it offers convenient #as_* cast methods.

Examples

metadata = Chem::Metadata.new

# four data types are supported
metadata["str"] = "Foo"
metadata["int"] = 123
metadata["float"] = 1.234
metadata["bool"] = true
# metadata["x"] = /[a-z]/ # fails to compile

# (base type) arrays are also supported
metadata["array_of_int"] = [1, 2, 3]
metadata["array_of_string"] = %w(1 2 3)
metadata["nested_array"] = [[1, 2], [3]]
# metadata["mixed_array"] = [1, "2", true] # does not compile

Values are stored as Any instances. Use #as_* cast methods get the actual value.

metadata["str"]             # => Chem::Metadata::Any("Foo")
metadata["str"].as_s.upcase # => "FOO"
metadata["str"].as_i?       # => nil
metadata["str"].as_i        # raises TypeCastError
metadata["str"].as_a        # raises TypeCastError

Arrays are returned as Array(Any). Use Array#map(&.as_*) or #as_a(type) to get a typed array.

metadata["array_of_int"].as_a             # => [Chem::Metadata::Any(1), ...]
metadata["array_of_int"].as_a.map(&.as_i) # => [1, 2, 3]
metadata["array_of_int"].as_a(Int32)      # => [1, 2, 3]
metadata["nested_array"].as_2a(Int32)     # => [[1, 2], [3]]

Included Modules

• Enumerable({String, Bool | Float64 | Int32 | String})
• Iterable({String, Bool | Float64 | Int32 | String})

Defined in:

Instance Method Summary

• #[](key : String) : Any

  Returns the value for the given key.

• #[]=(key : String, value : Bool) : Bool

  Sets the value of key to the given value.

• #[]=(key : String, value : Float64) : Float64

  Sets the value of key to the given value.

• #[]=(key : String, value : Int32) : Int32

  Sets the value of key to the given value.

• #[]=(key : String, value : String) : String

  Sets the value of key to the given value.

• #[]=(key : String, value : Array) : Array

  Sets the value of key to the given value.

• #[]?(key : String) : Any | Nil

  Returns the value for the given key.

• #clear : self

  Empties the Metadata and returns it.

• #delete(key : String) : Any | Nil

  Deletes the key-value pair and returns the value.

• #delete(key : String, & : String -> {String, Bool | Float64 | Int32 | String}) : Any | {String, Bool | Float64 | Int32 | String} forall T

  Deletes the key-value pair and returns the value.

• #each(& : Tuple(String, Any) -> ) : Nil

  Must yield this collection's elements to the block.

• #each : Iterator(Tuple(String, Any))

  Must return an Iterator over the elements in this collection.

• #each_key(& : String -> ) : Nil

  Yields each key to the given block.

• #each_key : Iterator(String)

  Returns an iterator over the keys.

• #each_value(& : Any -> ) : Nil

  Yields each value to the given block.

• #each_value : Iterator(Any)

  Returns an iterator over the values.

• #empty? : Bool

  Returns true when the metadata contains no key-value pairs, else false.

• #fetch(key : String, default : {String, Bool | Float64 | Int32 | String}) : Any | {String, Bool | Float64 | Int32 | String} forall T

  Returns the value if the given key exists, else default.

• #fetch(key : String, & : String -> {String, Bool | Float64 | Int32 | String}) : Any | {String, Bool | Float64 | Int32 | String} forall T

  Returns the value if the given key exists, else the value returned by the given block invoked with key.

• #has_key?(key : String) : Bool

  Returns true if key exists, else false.

• #has_value?(value : ValueType) : Bool

  Returns true if any key is associated with value, else false.

• #inspect(io : IO) : Nil

  Appends a String representation of this object which includes its class name, its object address and the values of all instance variables.

• #key_for(value : ValueType) : String

  Returns a key with the given value.

• #key_for(value : Bool, & : Bool -> {String, Bool | Float64 | Int32 | String}) : String | {String, Bool | Float64 | Int32 | String} forall T

  Returns a key with the given value.

• #key_for(value : Float64, & : Float64 -> {String, Bool | Float64 | Int32 | String}) : String | {String, Bool | Float64 | Int32 | String} forall T

  Returns a key with the given value.

• #key_for(value : Int32, & : Int32 -> {String, Bool | Float64 | Int32 | String}) : String | {String, Bool | Float64 | Int32 | String} forall T

  Returns a key with the given value.

• #key_for(value : String, & : String -> {String, Bool | Float64 | Int32 | String}) : String | {String, Bool | Float64 | Int32 | String} forall T

  Returns a key with the given value.

• #key_for?(value : ValueType) : String | Nil

  Returns a key with the given value, or nil if no key is associated with value.

• #keys : Array(String)

  Returns a new Array with all the keys.

• #merge!(other : self) : self

  Adds the contents of other to this metadata.

• #merge!(other : self, & : String, Any, Any -> _) : self

  Adds the contents of other to this metadata.

• #reject!(& : String, Any -> ) : self

  Deletes the entries for which the given block is truthy.

• #reject!(keys : Enumerable(String)) : self

  Deletes the entries for the given keys.

• #reject!(*keys : String) : self

  Deletes the entries for the given keys.

• #select!(& : String, Any -> ) : self

  Deletes every entry except for which the given block is falsey.

• #select!(keys : Enumerable(String)) : self

  Deletes every entry except for the given keys.

• #select!(*keys : String) : self

  Deletes every entry except for the given keys.

• #size : Int32

  Returns the number of key-value pairs.

• #to_a : Array(Tuple(String, Any))

  Returns an array containing key-value pairs as tuples.

• #to_s(io : IO) : Nil

  Appends a short String representation of this object which includes its class name and its object address.

• #update(key : String, & : Any -> ValueType) : Any

  Yields the value for the given key and updates it with the value returned by the given block.

• #values : Array(Any)

  Returns an array containing the values.

• #values_at(keys : Enumerable(String)) : Array(Any)

  Returns the values for the given keys.

• #values_at(*keys : String)

  Returns the values for the given keys.

Instance Method Detail

class Person
  def initialize(@name : String, @age : Int32)
  end
end

Person.new("John", 32).inspect # => #<Person:0x10fd31f20 @name="John", @age=32>

class Person
  def initialize(@name : String, @age : Int32)
  end
end

Person.new("John", 32).to_s # => #<Person:0x10a199f20>