From 14b93071eca21c69b635bd77eb68057b2906ddab Mon Sep 17 00:00:00 2001
From: Klaus Aehlig <klaus.aehlig@huawei.com>
Date: Mon, 22 Apr 2024 10:48:46 +0200
Subject: expressions: add "length" function

Lists are somtimes used in configurations as replacement for tuples.
Providing length gives an easy way to detect usage errors.
---
 src/buildtool/build_engine/expression/evaluator.cpp | 10 ++++++++++
 1 file changed, 10 insertions(+)

(limited to 'src')

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},
-- 
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