A value type stores its data directly, passes values by value, and copies the value when it moves between bindings or function calls. In F#, value types commonly appear through struct tuples and records marked with the [<Struct>] attribute. section 5.2.2 section 5.3.3
The choice is practical rather than automatically superior. Reference tuples incur garbage-collection costs, while value tuples incur copying costs, especially when they contain many fields. Prefer the ordinary reference representation unless measured performance evidence justifies the extra struct syntax. section 5.2.2
F# applies value-type syntax to two common data shapes:
- Use struct tuples when a tuple should have value semantics instead of the default reference semantics. section 5.2.2
- Add [<Struct>] to a record when the record itself should become a value type; benchmark before changing an established model. section 5.3.3
A struct tuple
let y = 1, 2 let x = struct (1, 2) The first expression creates an ordinary F# tuple; the second explicitly creates a value tuple. Struct annotations also affect how the tuple is deconstructed and annotated. section 11.1.4 section 5.2.2
let y = 1,2 #1 let x = struct (1,2) #2
Compare ordinary tuple construction with the explicit struct form. section 11.1.4
