C++ lambdas: how to make a function that takes a lambda expression?

Question

C++ / C#

I'm working with QAbstractItemModel and I have to do something like this.
• Test 1 failed → return QVariant().
• Test 2 failed → return QVariant().
All checks passed - we display some information.
Decided to rewrite this business on lambdas.
Let's simplify the task.

struct Entry {
  float lo, hi;
};

class GetData {
public:
  virtual QVariant get(const Entry& en) const = 0;
};

QVariant GetLo : public GetData {
public:
  QVariant get(const Entry& en) const override { return en.lo; }
  static const GetLo INSTANCE;
}

QVariant entryToVar(const Entry* en, const GetData& getData) {
  if (en == nullptr) return QVariant();
  return getData.get(*en);
}

…
QVariant vLo = entryToVar(pEntry, GetLo::INSTANCE);

How to rewrite all this in lambdas? What parameter to put instead of const GetData& getData?
If you make a template, under what conditions will the template unravel into the same thing?