A "runtime constant" is a static readonly field or static get-only property of a deeply immutable value or reference type, that is conceptually as constant as a named scalar or string declared with the const keyword.
The proposal is to allow such runtime constants to be used in case statements, pattern matching against, etc, for each operator the underlying type implements (equality, comparison).
Motivation: Simplifies many common patterns, enabling developers to declare constants of structured data types and have the same level of language support for them as for scalar and string constants.
Example: The main point in this example is that the named runtime constant cannot be represented with a single scalar or string, as its identity has two components, city name and state ID, and it also contains additional metadata, the geo-location. Without the proposed feature, developers currently have to resort to workarounds such as defining a parallel enum or string constants, in addition to the runtime constant, to be able to use the identity in a switch statement or pattern.
static readonly City BellevueWA = new City("Bellevue", "WA", 47.614444, -122.1925);
switch (address.city)
{
case BellevueWA: // if (address.city == BellevueWA)
...
}