Constr
Extends: PlutusData < Resource
Description
--- Introduction to algebraic types --- Plutus supports the use of so called "sum types" and "product types". These are part of a more general concept called "Algebraic Data Types" (or ADTs for short).[br][br]Products are more common in programming languages, so we start with them. A product type is the "combination" of multiple types to create a larger one containing all of its constituents. These are normally known as "tuples", "structs" or even "classes" (but without any of the methods!).[br][br]In GDScript, the closest thing to product types are classes (though this might change soon with the inclusion of structs):[br][br] [codeblock] class StringAndInt: var a_string: String var an_int: int [/codeblock] [br][br]In the previous example, the class we defined was the product of type [String] and type [int]. The central characteristic of products is that [b]one can always decompose them into their constituents[/b], i.e: one can always get the [String] and [int] out of a "StringAndInt" class.[br][br]Sum types can also be described as a "combination" of other types. However, in contrast to products, [b]one can only extract a single component of out of them[/b]. So the sum type that combines [String] and [int] would be called "String[b]Or[/b]Int". This SDK already uses sum types, like [Result], to encode different [b]exclusive[\b] possibilities [b]or choices[/b]. But sum types are not well supported by GDScript, so one must be careful not to try to extract the wrong component from a sum (since only one component can be extracted at any given time). In other languages, the language itself disallows access to the component without checking for its presence first (resulting in a static error).[br][br]--- How [Constr] works --- Plutus supports both sums and products with a single type: [Constr]. A [Constr] (from constructor) is a "sum of products" (or SOP). As the name suggests, it is possibly many products combined in a sum.[br][br]The reason this works for representing pure sums and pure products is that:[br][br] A pure product can be thought of as a sum with one choice, where that choice is a product composed of possibly many types.[br] A pure sum can be thought of as a sum with possibly many choices, where all the choices are basic, non-product types.[br][br]. And of course, any combination of sums and products that can be imagined is possible by nesting [Constr]s appropriately.[br][br]A [Constr] is built by providing an index (which represents the specific product selected) and an [Array] of fields (which represents the product itself). The index used for constructing a specific product is appropriately called "constructor".[br][br]--- Notes on ordering --- It may be obvious that the constructor index represents an ordered choice, and hence using a different index will create a different value:[br][br][code] Constr.new(BigInt.zero(), x) /= Constr.new(BigInt.one(), x) [/code][br][br]But it is worth mentioning this is also the case when changing the order of the fields:[br][br][code] Constr.new(BigInt.zero(), [x, y]) /= Constr.new(BigInt.zero(), [y, x]) [/code][br][br]The order of the fields [b]does[/b] change the product, so this is something very important to keep in mind when trying to encode/decode values from the blockchain.
--- Introduction to algebraic types --- Plutus supports the use of so called "sum types" and "product types". These are part of a more general concept called "Algebraic Data Types" (or ADTs for short).[br][br]Products are more common in programming languages, so we start with them. A product type is the "combination" of multiple types to create a larger one containing all of its constituents. These are normally known as "tuples", "structs" or even "classes" (but without any of the methods!).[br][br]In GDScript, the closest thing to product types are classes (though this might change soon with the inclusion of structs):[br][br] [codeblock] class StringAndInt: var a_string: String var an_int: int [/codeblock] [br][br]In the previous example, the class we defined was the product of type [String] and type [int]. The central characteristic of products is that [b]one can always decompose them into their constituents[/b], i.e: one can always get the [String] and [int] out of a "StringAndInt" class.[br][br]Sum types can also be described as a "combination" of other types. However, in contrast to products, [b]one can only extract a single component of out of them[/b]. So the sum type that combines [String] and [int] would be called "String[b]Or[/b]Int". This SDK already uses sum types, like [Result], to encode different [b]exclusive[\b] possibilities [b]or choices[/b]. But sum types are not well supported by GDScript, so one must be careful not to try to extract the wrong component from a sum (since only one component can be extracted at any given time). In other languages, the language itself disallows access to the component without checking for its presence first (resulting in a static error).[br][br]--- How [Constr] works --- Plutus supports both sums and products with a single type: [Constr]. A [Constr] (from constructor) is a "sum of products" (or SOP). As the name suggests, it is possibly many products combined in a sum.[br][br]The reason this works for representing pure sums and pure products is that:[br][br] A pure product can be thought of as a sum with one choice, where that choice is a product composed of possibly many types.[br] A pure sum can be thought of as a sum with possibly many choices, where all the choices are basic, non-product types.[br][br]. And of course, any combination of sums and products that can be imagined is possible by nesting [Constr]s appropriately.[br][br]A [Constr] is built by providing an index (which represents the specific product selected) and an [Array] of fields (which represents the product itself). The index used for constructing a specific product is appropriately called "constructor".[br][br]--- Notes on ordering --- It may be obvious that the constructor index represents an ordered choice, and hence using a different index will create a different value:[br][br][code] Constr.new(BigInt.zero(), x) /= Constr.new(BigInt.one(), x) [/code][br][br]But it is worth mentioning this is also the case when changing the order of the fields:[br][br][code] Constr.new(BigInt.zero(), [x, y]) /= Constr.new(BigInt.zero(), [y, x]) [/code][br][br]The order of the fields [b]does[/b] change the product, so this is something very important to keep in mind when trying to encode/decode values from the blockchain.
Method Descriptions
_init
A Constr.
get_constructor
Get the constructor index.
get_fields
Get the fields of the product.