gontract

gontract is a require-ensure-library for Go that provides a contract-programming framework. To enable partial Design by Contract (DbC), it aims to bridge the "procedural gap" in Go by providing explicit Require and Ensure checks for writing preconditions and postconditions naturally and idiomatically in Go .

• Contract Decoupling: Separating safety logic from business logic.
• Safety Assertions: Provides immediate feedback upon contract violation during development.

The typical use of gontract is to wrap the implementation body of a function in a Require-Ensure-sandwich. Here is an incomplete, non-working example to illustrate the idea:

func myfunc(args) {
// precondition(s):
Require(predicate, "message")
...
Require(predicate, "message")
// implementation
...
// postcondition(s):
Ensure(predicate, "message")
Ensure(predicate, "message")
...
}

A very natural pattern is to put postconditions into a defer statement like so:

func myfunc(args) {
// precondition(s):
Require(predicate, "message")
...
Require(predicate, "message")
...

// postcondition(s):
defer func() {

Ensure(predicate, "message")
...
Ensure(predicate, "message")

}()


// implementation
...
}

These examples are not intended to work, just to illustrate ideas.

For real, working examples, look into the examples folder

For interface-based designs, it is best to keep the interface itself plain and apply preconditions and postconditions in a wrapper implementation around the real implementation instead of clobbering the function implementations with the contract implementations using Require and Ensure.

The companion package github.com/gontract/gontract/ifacewrap provides small helpers for that style. Its declarative Requirements and Assurances run through gontract.Require and gontract.Ensure automatically, so wrapper code only needs to provide predicates and messages. See cmd/examples/ifacewrap_division for a minimal example.

In addition to ifacewrap, the companion package github.com/gontract/gontract/funcwrap provides helpers for defining a function along with its contract. See cmd/examples/funcwrap_division for a simple example.

A small math helper library has been split out of the division examples into a separate project manc.

To increase the cohesion but hopefully not the confusion, manc uses gontract for function contracts while being used in contract specifications in the division examples in the gontract projects itself.