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-rw-r--r--doc/concepts/expressions.md3
-rw-r--r--src/buildtool/build_engine/expression/evaluator.cpp10
-rw-r--r--test/buildtool/build_engine/expression/expression.test.cpp13
3 files changed, 26 insertions, 0 deletions
diff --git a/doc/concepts/expressions.md b/doc/concepts/expressions.md
index 80378191..a14cd60f 100644
--- a/doc/concepts/expressions.md
+++ b/doc/concepts/expressions.md
@@ -256,6 +256,9 @@ those) argument(s) to obtain the final result.
- `"reverse"` The argument has to be a list. The result is a new list
with the entries in reverse order.
+- `"length"` The argument has to be a list. The result is the length
+ of the list.
+
- `"++"` The argument has to be a list of lists. The result is
the concatenation of those lists.
diff --git a/src/buildtool/build_engine/expression/evaluator.cpp b/src/buildtool/build_engine/expression/evaluator.cpp
index f91e5b13..11299bb5 100644
--- a/src/buildtool/build_engine/expression/evaluator.cpp
+++ b/src/buildtool/build_engine/expression/evaluator.cpp
@@ -232,6 +232,15 @@ auto Reverse(ExpressionPtr const& expr) -> ExpressionPtr {
return ExpressionPtr{reverse_result};
}
+auto Length(ExpressionPtr const& expr) -> ExpressionPtr {
+ if (not expr->IsList()) {
+ throw Evaluator::EvaluationError{fmt::format(
+ "length expects list but instead got: {}.", expr->ToString())};
+ }
+ return ExpressionPtr{
+ static_cast<Expression::number_t>(expr->List().size())};
+}
+
auto NubRight(ExpressionPtr const& expr) -> ExpressionPtr {
if (not expr->IsList()) {
throw Evaluator::EvaluationError{fmt::format(
@@ -1098,6 +1107,7 @@ auto const kBuiltInFunctions =
{"enumerate", UnaryExpr(Enumerate)},
{"set", UnaryExpr(Set)},
{"reverse", UnaryExpr(Reverse)},
+ {"length", UnaryExpr(Length)},
{"values", UnaryExpr(Values)},
{"lookup", LookupExpr},
{"[]", ArrayAccessExpr},
diff --git a/test/buildtool/build_engine/expression/expression.test.cpp b/test/buildtool/build_engine/expression/expression.test.cpp
index 18189baf..83550ebd 100644
--- a/test/buildtool/build_engine/expression/expression.test.cpp
+++ b/test/buildtool/build_engine/expression/expression.test.cpp
@@ -1010,6 +1010,19 @@ TEST_CASE("Expression Evaluation", "[expression]") { // NOLINT
)"_json));
}
+ SECTION("length expression") {
+ auto expr = Expression::FromJson(R"(
+ { "type": "length"
+ , "$1": ["foo", "bar", "baz"]
+ }
+ )"_json);
+ REQUIRE(expr);
+
+ auto result = expr.Evaluate(env, fcts);
+ REQUIRE(result);
+ CHECK(result == Expression::FromJson("3"_json));
+ }
+
SECTION("keys expression") {
auto expr = Expression::FromJson(R"(
{ "type": "keys"