What

• Patterns are a syntactic category in the Dart language, like statements and expressions.

• A pattern may match a value and / or destructure a value.

• Patter matching check whether a given value: a> Has a certain shape (form). b> Is a certain constant. c> Is equal to something else. d> Has a certain type.

• When an object matches a pttern, the pattern can then access the object’s data and extract it in parts, whcih we call destructuring.

• Patterns can be nested, no matter for maching patterns or destructuring patterns:

    switch (list) {
        case ['a' || 'b', var c]:
        print(c);
    }
  

• Patterns can appear in: a> Local variable declarations and assignments b> for and for-in loops c> if-case and switch-case d> Control flow in collection literals. This refers to case pattern that is refutable, which means either have a match or skip and continue if there is no match.

Why

Pattern Types

See all the possible pattern types here: https://dart.dev/language/pattern-types. Notice, those pattern can be nested together.

Sealed Class

sealed is a class modifier, which is used to create a known, enumerable set of subtypes. This allows you to create a switch over those subtypes that is statically ensured to be “exhaustive”. Because it prevents a class from being extended or implemented “outside” its own library. Sealed classes are implicitly abstract.

Switch Expression

• switch expression can be used wherever Dart allows expressions, except at the start of an expression statement, where a switch statement should be used instead.

• The syntax of a switch expression differs from switch statement syntax: a> Cases do not start with the case keyword. b> A case body is a single expression instead of a series of statements. c> Each case must have a body; there is no implicit fallthrough for empty cases. d> Case patterns are separated from their bodies using => instead of :. e> Cases are separated by , (and an optional trailing , is allowed). f> Default cases can only use _, instead of allowing both default and _.

• switch expression / statement can be used with guard clause.

How

Where

When

Who