The bool strategy

The bool strategy can be applied to fields of type bool.

fields {
    #[sharding(bool)]
    pub field: bool,
}

Tokens. VerusSync creates a fresh token type, tok, named State::field where State is the name of the VerusSync system and field is the name of the field.

The token type tok implements the UniqueSimpleToken trait.

Relationship between global field value and the token. When field is false, this corresponds to no token existing, while when field is true, this corresponds to a token existing. The token doesn’t contain any additional data. Having multiple such tokens at the same time is an impossible state.

Manipulation of the field

Quick Reference

In the following table, b: bool.

Command Meaning in transition Exchange Fn Parameter
init field = b; init field = b; Output Option<tok>
remove field -= true; require field == true;
update field = false;		 Input tok
have field >= true; require field == true; Input &tok
add field += true; assert field == false;
update field = true;		 Output tok
remove field -= (b); require (b ==> field); update field = field && !b; Input Option<tok>
have field >= (b); require (b ==> field); Input &Option<tok>
add field += (b); assert !(field && b); update field = field || b; Output Option<tok>

Initializing the field

Initializing the field is done with the usual init statement (as it for all strategies).

init field = b;

The instance-init function will return a token of type Option<tok>, related as follows:

value of b: bool    value of optional token Option<tok>
false None
true Some(tok) where tok.value() == v

Adding a token

To write an operation that creates a token, equivalently, updating the field’s value from false to true, write, inside any transition! operation:

add field += true;

This operation has an inherent safety condition that the prior value of field is false. The resulting token exchange function will return a token of type tok.

Removing a token

To write an operation that removes a token, equivalently, updating the field’s value from true to false, write, inside any transition! operation:

remove field -= true;

The resulting exchange function will consume a tok token as a parameter.

Checking the value of the token

To check the value of the token without removing it, write, inside any transition!, readonly! or property! operation:

have field >= true;

The resulting exchange function will accept an immutable reference &tok (that is, it takes the token as input but does not consume it).

Operations that manipulate optional tokens

You can also write versions of the above operations that operate on optional tokens. The operations below are equivalent to the above versions whenever b == true, and they are all no-ops when b == false.

To create an Option<tok>:

add field += (b);

To consume an Option<tok>:

remove field -= (b);

To check the value of an &Option<tok>:

have field >= (b);

The value of b is related to the value of Option<tok> as they are for initialization.

Example

TODO