UPVALUE Meaning and
Definition
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An "upvalue" refers to a programming term commonly used in languages that support closures, such as Lua. It is essentially a variable that is accessible from an inner function or closure even after the parent function has finished executing. In other words, it is a local variable that remains in memory and retains its value for subsequent invocations of the parent function.
When a function with an upvalue is created, the upvalue is allocated in memory along with the function itself. The inner function can access and modify the upvalue, and any changes made to it will persist across different invocations of the outer function.
Upvalues are useful in situations where functions need to retain state or carry additional information beyond their arguments. They provide a way for inner functions to access and manipulate variables that are local to the outer function, enhancing flexibility and enabling more efficient code organization.
Although similar in concept to a closure, an upvalue should be distinguished from an enclosing environment. An upvalue represents the actual value or reference being captured, while the enclosing environment encompasses the variables and their values that are accessible to a closure.
In summary, an upvalue is a variable in a programming language that allows an inner function to access and maintain a value from an outer function, even after the outer function has finished executing. It simplifies coding by preserving variable values between function invocations and provides a powerful tool to handle state and maintain context.
Etymology of UPVALUE
The term "upvalue" was coined by Guy L. Steele Jr. in the programming language Lisp in the early 1970s. The word is a combination of "up" and "value".
In programming languages, a variable typically holds a value that can be changed or accessed. However, in Lisp, an "upvalue" is created when a function refers to a variable defined in an outer function that has already returned. The upvalue retains its value even after the outer function has completed.
The term "upvalue" reflects the concept that the variable's value is looked up in an "upward" direction, rather than being a traditional variable with a fixed value. It distinguishes this type of variable from a regular global or local variable. As Lisp heavily influenced the development of subsequent programming languages, "upvalue" became a commonly used term in several other languages.
Conjugate verb Upvalue
CONDITIONAL
I
would upvalue
you
would upvalue
he/she/it
would upvalue
we
would upvalue
they
would upvalue
CONDITIONAL CONTINUOUS
I
would be upvaluing
you
would be upvaluing
he/she/it
would be upvaluing
we
would be upvaluing
they
would be upvaluing
CONDITIONAL PERFECT
I
would have upvalue
you
would have upvalue
he/she/it
would have upvalue
we
would have upvalue
they
would have upvalue
CONDITIONAL PERFECT CONTINUOUS
I
would have been upvaluing
you
would have been upvaluing
he/she/it
would have been upvaluing
we
would have been upvaluing
they
would have been upvaluing
FUTURE
I
will upvalue
you
will upvalue
he/she/it
will upvalue
we
will upvalue
they
will upvalue
FUTURE CONTINUOUS
I
will be upvaluing
you
will be upvaluing
he/she/it
will be upvaluing
we
will be upvaluing
they
will be upvaluing
FUTURE PERFECT
I
will have upvalued
you
will have upvalued
he/she/it
will have upvalued
we
will have upvalued
they
will have upvalued
FUTURE PERFECT CONTINUOUS
I
will have been upvaluing
you
will have been upvaluing
he/she/it
will have been upvaluing
we
will have been upvaluing
they
will have been upvaluing
IMPERATIVE
you
upvalue
we
let´s upvalue
to upvalue
PAST
I
upvalued
you
upvalued
he/she/it
upvalued
we
upvalued
they
upvalued
PAST CONTINUOUS
I
was upvaluing
you
were upvaluing
he/she/it
was upvaluing
we
were upvaluing
they
were upvaluing
PAST PARTICIPLE
upvalued
PAST PERFECT
I
had upvalued
you
had upvalued
he/she/it
had upvalued
we
had upvalued
they
had upvalued
PAST PERFECT CONTINUOUS
I
had been upvaluing
you
had been upvaluing
he/she/it
had been upvaluing
we
had been upvaluing
they
had been upvaluing
PRESENT
I
upvalue
you
upvalue
he/she/it
upvalues
we
upvalue
they
upvalue
PRESENT CONTINUOUS
I
am upvaluing
you
are upvaluing
he/she/it
is upvaluing
we
are upvaluing
they
are upvaluing
PRESENT PARTICIPLE
upvaluing
PRESENT PERFECT
I
have upvalued
you
have upvalued
he/she/it
has upvalued
we
have upvalued
they
have upvalued
PRESENT PERFECT CONTINUOUS
I
have been upvaluing
you
have been upvaluing
he/she/it
has been upvaluing
we
have been upvaluing
they
have been upvaluing
