conditional_access_fun.cs

var x = e as T;
if (x != null) {
  ...
} else {
  // no usages of 'x' here
}
// no usages of 'x' here too

// =>

if (e is T x) {
  ...
}

/////////////////////////

if (x != null && x is T t)
// =>
if (x is T t)

//////////////////////////////////

if (x is T && x is T t)
// =>
if (x is T t)

//////////////////////////////////

if (x is T t && ((T) x).P != null)
// => NOT - can't be merged with (try)cast if 'is' introducing name
if ((x as T).P != null

//////////////////////////////////

if (x is T t && t.P != null)
// => BUT only if 't' is not used + first looks better!
if ((x as T)?.P != null)

/////////////////////////////

if (x == null) {
  return e;
}

return x; // or 'x.NotNullMember();'

// or

if (x != null) {
  return x; // or 'x.NotNullMember();'
}

return e;

// =>

return x ?? e;

////////////////////////////////////

T x = null;
if (e != null) x = e.P;

// =>

T x = e?.P;
// or
T x = e != null ? e.P : null; // check can derive type

////////////////////////////////////

if ((T as x)?.P is U) {
  var p = (U) ((T)x).P;
}

// =>

if ((T as x)?.P is U u) {
  var p = u;
}

////////////////////////////////////

while (index < statements.Count && statements[index] is ISwitchLabelStatement)
  cases.Add((ISwitchLabelStatement) statements[index]);

while (index < statements.Count && statements[index] is ISwitchLabelStatement sw)
  cases.Add(sw);

///////////////////////////////////

var xs = new List<FooNode>();
for (var node = x; node is FooNode; node = ((FooNode) node).Parent) {
  xs.Add((FooNode) node);
}

for (var node = x; node is FooNode foo; node = foo.Parent) {
  xs.Add(foo);
}

///////////////////////////////////

CA "Null propagation to 'if' statement"