Lock T, Lock F, or Create Locked Constants

The lock_TF() function locks the T and F values and sets them to TRUE and FALSE, respectively, to prevent the user from re-assigning them.
Removing the created T and F objects allows re-assignment again.

The X %<-c% A operator creates a constant X and assigns A to it.
Constants cannot be changed, only accessed or removed. So if you have a piece of code that requires some unchangeable constant, use this operator to create said constant.
Removing constant X also removes its binding lock. Thus to change a constant, simply remove it and re-create it.

Usage

lock_TF(env)

X %<-c% A

Arguments

env: an optional environment to give, determining in which environment T and F should be locked.
When not specified, the current environment is used.
X: a syntactically valid unquoted name of the object to be created.
A: any kind of object to be assigned to X.

Value

For lock_TF():

Two constants, namely T and F, set to TRUE and FALSE respectively, are created in the specified or else current environment, and locked. Removing the created T and F objects allows re-assignment again.

For X %<-c% A:

The object X containing A is created in the current environment, and this object cannot be changed. It can only be accessed or removed.

Details

Note that following statement

x %<-c% 2+2
print(x)

returns

[1] 2

due to R's precedence rules. Therefore, in such cases, the right hand side of X %<-c% A need to be surrounded with brackets. I.e.:

x %<-c% (2 + 2)

Note that the lock_TF() function and %s<-c% operator create constants through lockBinding.
The constants are protected from modification by copy, but they are not protected from modification by reference (see for example collapse::setv).

Examples


lock_TF()
X %<-c% data.frame(x = 3, y = 2) # this data.frame cannot be changed. Only accessed or removed.
X[1, ,drop=FALSE]
#>   x y
#> 1 3 2