patch 8.2.1794: no falsy Coalescing operator
Problem: No falsy Coalescing operator.
Solution: Add the "??" operator. Fix mistake with function argument count.
diff --git a/runtime/doc/eval.txt b/runtime/doc/eval.txt
index 6bf205d..b2b1600 100644
--- a/runtime/doc/eval.txt
+++ b/runtime/doc/eval.txt
@@ -133,7 +133,27 @@
:" executed
To test for a non-empty string, use empty(): >
:if !empty("foo")
-<
+
+< *falsy* *truthy*
+An expression can be used as a condition, ignoring the type and only using
+whether the value is "sort of true" or "sort of false". Falsy is:
+ the number zero
+ empty string, blob, list or dictionary
+Other values are truthy. Examples:
+ 0 falsy
+ 1 truthy
+ -1 truthy
+ 0.0 falsy
+ 0.1 truthy
+ '' falsy
+ 'x' truthy
+ [] falsy
+ [0] truthy
+ {} falsy
+ #{x: 1} truthy
+ 0z falsy
+ 0z00 truthy
+
*non-zero-arg*
Function arguments often behave slightly different from |TRUE|: If the
argument is present and it evaluates to a non-zero Number, |v:true| or a
@@ -877,10 +897,13 @@
All expressions within one level are parsed from left to right.
-expr1 *expr1* *trinary* *E109*
+expr1 *expr1* *trinary* *falsy-operator* *E109*
-----
-expr2 ? expr1 : expr1
+The trinary operator: expr2 ? expr1 : expr1
+The falsy operator: expr2 ?? expr1
+
+Trinary operator ~
The expression before the '?' is evaluated to a number. If it evaluates to
|TRUE|, the result is the value of the expression between the '?' and ':',
@@ -903,6 +926,23 @@
You should always put a space before the ':', otherwise it can be mistaken for
use in a variable such as "a:1".
+Falsy operator ~
+
+This is also known as the "null coalescing operator", but that's too
+complicated, thus we just call it the falsy operator.
+
+The expression before the '??' is evaluated. If it evaluates to
+|truthy|, this is used as the result. Otherwise the expression after the '??'
+is evaluated and used as the result. This is most useful to have a default
+value for an expression that may result in zero or empty: >
+ echo theList ?? 'list is empty'
+ echo GetName() ?? 'unknown'
+
+These are similar, but not equal: >
+ expr2 ?? expr1
+ expr2 ? expr2 : expr1
+In the second line "expr2" is evaluated twice.
+
expr2 and expr3 *expr2* *expr3*
---------------