Nevertheless De Morgans’s Law is one of those things from my days as an electronics research technician that’s still useful today – so it was worth it.
I needed to change an if statement around. Originally it was like this;
if (null == cert || !cert.HasPrivateKey) doMainPart() else doElsePart()
But I wanted to switch the main and else part around, so I wanted to reverse the result of the condition. I could have done this…
if ( !(null == cert || !cert.HasPrivateKey))
But instead I employed De Morgan’s Law. To invert the meaning of the entire condition the first step is to invert the meaning of each individual term of the condition. So:
null == certbecomes
null != cert
The second step is to change the operators that combine the terms, so
AND and vice-versa.
(null != cert && cert.HasPrivateKey) gives the exact opposite result to
(null == cert || !cert.HasPrivateKey).
if (null != cert && cert.HasPrivateKey) doElsePart() else doMainPart()
It’s really easy to tie yourself in knots with this kind of stuff, remembering De Morgan’s law can save a lot of heartache.
If you’re wondering why it’s “break the line, change the sign” this is because of the way boolean logic is written is electronics: if you want to invert the meaning of something you don’t put a ! in front of it, you draw a line over the top of it.
So our condition would have started as:
null == cert ||
We then want to invert the entire operation, so we draw a line right over the top…
Now we apply De Morgans’s Law, we break the line and change the sign.
Of course the two inversions on the right-hand side cancel each other out, so we finish with:
Of in C#
null != cert && cert.HasPrivateKey