feat(docs): empty contract parameters (#2346)

dev-docs/CHANGELOG.md

@@ -11,6 +11,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 - Added descriptions for `&&=`, `||=`, `>>=` and `<<=` augmented assignment operators: PR [#2328](https://github.com/tact-lang/tact/pull/2328)
 - Added gas best practices page: PR [#2342](https://github.com/tact-lang/tact/pull/2342)
+- Documented semantics of empty contract parameters: PR [#2346](https://github.com/tact-lang/tact/pull/2346)
 
 ### Release contributors
 

docs/src/content/docs/book/contracts.mdx

@@ -175,7 +175,7 @@ contract ContractParameters(
 
 State variables declared in this way have **no** default value. Instead, they get their initial data only when the contract is deployed, which is much cheaper compared to deployments with an extra initialization step in the [`init(){:tact}`](#init-function) function.
 
-The use of contract parameters syntax conflicts with using an [`init(){:tact}`](#init-function) function or declaring persistent state variables via the [contract fields syntax](#variables). Whenever possible, prefer using contract parameters unless you need specific on-chain deployment logic that must be run exactly once, i.e. via the [`init(){:tact}`](#init-function) function.
+The use of contract parameters syntax conflicts with using an `init(){:tact}` function or declaring persistent state variables via the [contract fields syntax](#variables). Whenever possible, prefer using contract parameters unless you need specific on-chain deployment logic that must be run exactly once, i.e. via the `init(){:tact}` function.
 
 ```tact
 contract ParamParamParam(
@@ -187,6 +187,21 @@ contract ParamParamParam(
 }
 ```
 
+An empty parameter list is still a parameter list, meaning that the contract won't have an implicit or explicit `init(){:tact}` function and will enjoy storage write optimizations. Removing the empty list makes a contract use the delayed initialization with an implicit `init(){:tact}` function.
+
+```tact
+contract StillParam() {
+    // COMPILATION ERROR! init() cannot be used along with contract parameters
+    init() {}
+}
+
+contract LazyInit {
+    // Everything's ok, and the following init() is redundant because there
+    // would be an implicit empty init() anyway in the absence of contract parameters.
+    init() {}
+}
+```
+
 :::note
 
   To obtain the initial state of the target contract in [internal functions](#internal-functions), [receivers](#receiver-functions), or [getters](#getter-functions), use the [`initOf{:tact}`](/book/expressions#initof) expression.
@@ -373,6 +388,21 @@ contract ParamParamParam(
 }
 ```
 
+Note that even an empty contract parameter list counts as using [contract parameters syntax](#parameters) and means that the contract won't have any variables in its persistent state. Removing the empty list makes a contract use the delayed initialization with an implicit `init(){:tact}` function.
+
+```tact
+contract StillParam() {
+    // COMPILATION ERROR! init() cannot be used along with contract parameters
+    init() {}
+}
+
+contract LazyInit {
+    // Everything's ok, and the following init() is redundant because there
+    // would be an implicit empty init() anyway in the absence of contract parameters.
+    init() {}
+}
+```
+
 :::note
 
   To obtain the initial state of the target contract in [internal functions](#internal-functions), [receivers](#receiver-functions), or [getters](#getter-functions), use the [`initOf{:tact}`](/book/expressions#initof) expression.