To add some info to an already perfect explanation 
A Lambda is more or less the c++ way to write a function inside a function.
Instead of doing this:
bool UMyClass::DoThis() {
// DoStuff
return DoThat();
}
you can do
bool UMyClass::DoThis() {
auto DoThat = []() -> bool {
return true;
};
return DoThat();
}
Sometimes you need the "-> " this is called a trailing type.
You can also call a lambda recursively by passing a lambda into itself:
auto HidePropertiesRecursive = [&DetailBuilder](auto&& HidePropertiesRecursive, const FString& InPropertyName, const UClass* InContainerClass) {
// DoStuff
HidePropertiesRecursive(HidePropertiesRecursive, PropPath, InContainerClass);
};
About the parameter naming of lambdas… I’m a bit bothered by “InHIt” as well but it really depends on what style you are using through the entire source code, you should keep that consistent. I reserve “In, Ref, Out” for method parameters but in loops and lambdas I like to remove that prefix and Suffix with an X to remind myself I am doing something in a loop.
for (AActor* ActorX : AllActors) {
}