docs: add tutorial

1 files changed, 74 insertions, 0 deletions

diff --git a/tutorial/04_conditions.sfinae b/tutorial/04_conditions.sfinae
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+// lesson 4: conditions
+//
+// a condition is ::true_type::value, ::false_type::value, ::equal<V, V>::value,
+// ::less<V, V>::value, or ::is_same<T, T>::value. the ::value is mandatory
+// a condition without it is a type, and a type is not a condition.
+
+// ::conditional_t<C, T, T> picks a type. this prints 1
+
+::emit<
+    ::conditional_t<
+        ::true_type::value,
+        ::decltype(::difference<'B', 'A'>),
+        ::void
+    >
+>::commit;
+
+// this picks ::void, and emitting ::void prints nothing at all. not even a newline
+
+::emit<
+    ::conditional_t<
+        ::less<
+            ::difference<'B', 'A'>,
+            ::difference<'A', 'A'>
+        >::value,
+        ::decltype(::difference<'Z', 'A'>),
+        ::void
+    >
+>::commit;
+
+// ::enable_if_t<C, ::sequence<...>> runs the statements when C holds
+// the statements inside a sequence are separated by commas, and each one is
+// still committed on its own
+
+::enable_if_t<
+    ::is_same<
+        ::remove_cv_t<::int32_t>,
+        ::int32_t
+    >::value,
+    ::sequence<
+        ::emit<
+            ::tuple<
+        ::integral_constant<::char, ::difference<'s', '\0'>>,
+        ::integral_constant<::char, ::difference<'a', '\0'>>,
+        ::integral_constant<::char, ::difference<'m', '\0'>>,
+        ::integral_constant<::char, ::difference<'e', '\0'>>
+            >
+        >::commit
+    >
+>::commit;
+
+// ::static_assert<C> stops the program when C does not hold. it does this at
+// runtime, because that is when we know
+
+::static_assert<
+    ::equal<
+        ::difference<'C', 'A'>,
+        ::sum<
+            ::difference<'B', 'A'>,
+            ::difference<'B', 'A'>
+        >
+    >::value
+>::commit;
+
+// ::conditional<C, V, V> is the same idea for values. this prints 9
+
+::emit<
+    ::decltype(
+        ::conditional<
+            ::false_type::value,
+            ::difference<'A', 'A'>,
+            ::difference<'J', 'A'>
+        >
+    )
+>::commit;