feat: add instance-based overloads for table_constraint functions

Add instance-based overloads for primary_key, key, unique_key,
fulltext_key, and spatial_key so columns can be passed as instances
instead of template parameters:

  primary_key(col{})
  key(index_id<"idx">{}, col{})
  unique_key(index_id<"uq">{}, col1{}, col2{})

Template-only forms are preserved for backward compatibility.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: Pierre-Luc Gagné

CHANGELOG.md

@@ -8,6 +8,10 @@ Versioning follows [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
 ## [Unreleased]
 
+### Added
+
+- Instance-based overloads for `table_constraint::primary_key`, `key`, `unique_key`, `fulltext_key`, `spatial_key` — e.g. `primary_key(col{})` and `key(index_id<"idx">{}, col{})` as alternatives to the template-only forms
+
 ---
 
 ## [4.0.0] – 2026-03-29

lib/include/ds_mysql/sql_ddl.hpp

@@ -116,30 +116,60 @@ template <ColumnDescriptor... Cols>
     return "PRIMARY KEY " + columns_sql<Cols...>();
 }
 
+template <ColumnDescriptor... Cols>
+    requires(sizeof...(Cols) > 0)
+[[nodiscard]] inline std::string primary_key(Cols const&...) {
+    return "PRIMARY KEY " + columns_sql<Cols...>();
+}
+
 template <ColumnDescriptor... Cols, fixed_string Name>
     requires(sizeof...(Cols) > 0)
 [[nodiscard]] inline std::string key(index_id<Name> const&) {
     return "KEY " + std::string(Name) + ' ' + columns_sql<Cols...>();
 }
 
+template <fixed_string Name, ColumnDescriptor... Cols>
+    requires(sizeof...(Cols) > 0)
+[[nodiscard]] inline std::string key(index_id<Name> const&, Cols const&...) {
+    return "KEY " + std::string(Name) + ' ' + columns_sql<Cols...>();
+}
+
 template <ColumnDescriptor... Cols, fixed_string Name>
     requires(sizeof...(Cols) > 0)
 [[nodiscard]] inline std::string unique_key(index_id<Name> const&) {
     return "UNIQUE KEY " + std::string(Name) + ' ' + columns_sql<Cols...>();
 }
 
+template <fixed_string Name, ColumnDescriptor... Cols>
+    requires(sizeof...(Cols) > 0)
+[[nodiscard]] inline std::string unique_key(index_id<Name> const&, Cols const&...) {
+    return "UNIQUE KEY " + std::string(Name) + ' ' + columns_sql<Cols...>();
+}
+
 template <ColumnDescriptor... Cols, fixed_string Name>
     requires(sizeof...(Cols) > 0)
 [[nodiscard]] inline std::string fulltext_key(index_id<Name> const&) {
     return "FULLTEXT KEY " + std::string(Name) + ' ' + columns_sql<Cols...>();
 }
 
+template <fixed_string Name, ColumnDescriptor... Cols>
+    requires(sizeof...(Cols) > 0)
+[[nodiscard]] inline std::string fulltext_key(index_id<Name> const&, Cols const&...) {
+    return "FULLTEXT KEY " + std::string(Name) + ' ' + columns_sql<Cols...>();
+}
+
 template <ColumnDescriptor... Cols, fixed_string Name>
     requires(sizeof...(Cols) > 0)
 [[nodiscard]] inline std::string spatial_key(index_id<Name> const&) {
     return "SPATIAL KEY " + std::string(Name) + ' ' + columns_sql<Cols...>();
 }
 
+template <fixed_string Name, ColumnDescriptor... Cols>
+    requires(sizeof...(Cols) > 0)
+[[nodiscard]] inline std::string spatial_key(index_id<Name> const&, Cols const&...) {
+    return "SPATIAL KEY " + std::string(Name) + ' ' + columns_sql<Cols...>();
+}
+
 // Accepts a check_expr predicate; column name, operator, and value are all
 // derived from the typed predicate.
 //

tests/unit/test_ddl.cpp

@@ -241,8 +241,8 @@ template <>
 struct ds_mysql::table_constraints<symbol_with_indexes> {
     static std::vector<std::string> get() {
         return {
-            table_constraint::primary_key<symbol_with_indexes::id>(),
-            table_constraint::key<symbol_with_indexes::exchange_id>(index_id<"index_exchange_id">{}),
+            table_constraint::primary_key(symbol_with_indexes::id{}),
+            table_constraint::key(index_id<"index_exchange_id">{}, symbol_with_indexes::exchange_id{}),
         };
     }
 };
@@ -265,7 +265,7 @@ template <>
 struct ds_mysql::table_constraints<audit_log> {
     static std::vector<std::string> get() {
         return {
-            table_constraint::primary_key<audit_log::id>(),
+            table_constraint::primary_key(audit_log::id{}),
         };
     }
 };
@@ -753,11 +753,11 @@ suite<"DDL"> ddl_suite = [] {
     };
 
     "table_constraint helper SQL fragments - renders UNIQUE/FULLTEXT/SPATIAL"_test = [] {
-        expect(table_constraint::unique_key<test_table::name>(index_id<"uq_test_name">{}) ==
+        expect(table_constraint::unique_key(index_id<"uq_test_name">{}, test_table::name{}) ==
                "UNIQUE KEY uq_test_name (name)"s);
-        expect(table_constraint::fulltext_key<test_table::name>(index_id<"ft_test_name">{}) ==
+        expect(table_constraint::fulltext_key(index_id<"ft_test_name">{}, test_table::name{}) ==
                "FULLTEXT KEY ft_test_name (name)"s);
-        expect(table_constraint::spatial_key<test_table::id>(index_id<"sp_test_id">{}) ==
+        expect(table_constraint::spatial_key(index_id<"sp_test_id">{}, test_table::id{}) ==
                "SPATIAL KEY sp_test_id (id)"s);
     };