LESSCSS: Assign a value to a property taken from another one's - less

Question

In some cases is common to use same values in different properties, for example (is just an example to show purpose) the following nested rule:
.button-link
{
height:40px;
a
{
line-height:40px;
}
}
The idea is that to vertically center button text line-height and height should be equal.
Is there a way in LESS to "assign a value taken from a diffent property"?
I know that I should use a LESS #variable but in this case is not the same thing and need extra code. Instead should very interesting and useful if I should edit only button's height and then LESS will replaced the same value to line-height
UPDATE:
Another example could be the following:
.button-link
{
color:white;
background:black;
&:hover
{
color:black;
background:white;
}
}
In which "hover" status should invert color and background-color comparing to default state.

Answer 1

This is possible starting with v3 of LESS! Here is the documentation on it.
The example use case they provide ends up with the background-color getting the same value as the color property when compiled:
.widget {
color: #efefef;
background-color: $color;
}

Answer 2

You can´t :(. What i usually do is:
#buttom-height = 100px;
#a-link-height: #buttom-height;
and use that variables in your less declarations. Its a dummy example, i know, but imagine calculated data values from other variables or complex dependencies, proportional paddings/margins... that´s the way i learnt from Bootstrap LESS code.