String: Add .is-empty and .character-count properties

Introduce two new properties for string in .slint: - .is-empty: Checks if a string is empty. - .character-count: Retrieves the number of grapheme clusters https://www.unicode.org/reports/tr29/#Grapheme_Cluster_Boundaries These additions enhance functionality and improve convenience when working with string properties.
slint-ui · Jan 6, 2025 · ebb5d3f · ebb5d3f
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diff --git a/api/cpp/Cargo.toml b/api/cpp/Cargo.toml
@@ -62,6 +62,7 @@ image = { workspace = true, optional = true, features = ["default"] }
 
 esp-backtrace = { version = "0.14.0", features = ["panic-handler", "println"], optional = true }
 esp-println = { version = "0.12.0", default-features = false, features = ["uart"], optional = true }
+unicode-segmentation = "1.12.0"
 
 [build-dependencies]
 anyhow = "1.0"

diff --git a/api/cpp/lib.rs b/api/cpp/lib.rs
@@ -152,6 +152,11 @@ pub extern "C" fn slint_string_to_float(string: &SharedString, value: &mut f32)
     }
 }
 
+#[no_mangle]
+pub extern "C" fn slint_string_character_count(string: &SharedString) -> usize {
+    unicode_segmentation::UnicodeSegmentation::graphemes(string.as_str(), true).count()
+}
+
 #[no_mangle]
 pub extern "C" fn slint_string_to_usize(string: &SharedString, value: &mut usize) -> bool {
     match string.as_str().parse::<usize>() {

diff --git a/api/rs/slint/Cargo.toml b/api/rs/slint/Cargo.toml
@@ -187,6 +187,8 @@ log = { workspace = true, optional = true }
 
 raw-window-handle-06 = { workspace = true, optional = true }
 
+unicode-segmentation = "1.12.0"
+
 [target.'cfg(not(target_os = "android"))'.dependencies]
 # FemtoVG is disabled on android because it doesn't compile without setting RUST_FONTCONFIG_DLOPEN=on
 # end even then wouldn't work because it can't load fonts

diff --git a/api/rs/slint/private_unstable_api.rs b/api/rs/slint/private_unstable_api.rs
@@ -230,5 +230,6 @@ pub mod re_exports {
     pub use once_cell::race::OnceBox;
     pub use once_cell::unsync::OnceCell;
     pub use pin_weak::rc::PinWeak;
+    pub use unicode_segmentation::UnicodeSegmentation;
     pub use vtable::{self, *};
 }
diff --git a/docs/astro/src/content/docs/reference/primitive-types.mdx b/docs/astro/src/content/docs/reference/primitive-types.mdx
@@ -20,6 +20,11 @@ boolean whose value can be either `true` or `false`.
 <SlintProperty propName="string" typeName="string" defaultValue='""'>
 Any sequence of utf-8 encoded characters surrounded by quotes is a `string`: `"foo"`.
 
+```slint
+export component Example inherits Text {
+    text: "hello";
+}
+```
 Escape sequences may be embedded into strings to insert characters that would
 be hard to insert otherwise:
 
@@ -33,15 +38,36 @@ be hard to insert otherwise:
 
 Anything else following an unescaped `\` is an error.
 
+:::note[Note]
+  The `\{...}` syntax is not valid within the `slint!` macro in Rust.
+:::
+
+
+`is-empty` property is true when `string` doesn't contain anything.
+
 ```slint
-export component Example inherits Text {
-    text: "hello";
+export component LengthOfString {
+    property<bool> empty "".is-empty; // true
+    property<bool> not-empty: "hello".is-empty; // false
+}
+```
+
+`length` property returns number of [grapheme clusters](https://www.unicode.org/reports/tr29/#Grapheme_Cluster_Boundaries).
+
+```slint
+export component LengthOfString {
+    property<int> empty: "".length; // 0
+    property<int> hello: "hello".length; // 5
+    property<int> hiragana: "あいうえお".length; // 5
+    property<int> surrogate-pair: "😊𩸽".length; // 2
+    property<int> variation-selectors: "👍🏿".length; // 1
+    property<int> combining-character: "パ".length; // 1
+    property<int> zero-width-joiner: "👨‍👩‍👧‍👦".length; // 1
+    property<int> region-indicator-character: "🇦🇿🇿🇦".length; // 2
+    property<int> emoji-tag-sequences: "🏴󠁧󠁢󠁥󠁮󠁧󠁿".length; // 1
 }
 ```
 
-:::note[Note]
-  The `\{...}` syntax is not valid within the `slint!` macro in Rust.
-:::
 </SlintProperty>
 
 ## Numeric Types

diff --git a/internal/compiler/expression_tree.rs b/internal/compiler/expression_tree.rs
@@ -52,6 +52,10 @@ pub enum BuiltinFunction {
     StringToFloat,
     /// the "42".is_float()
     StringIsFloat,
+    /// the "42".is_empty
+    StringIsEmpty,
+    /// the "42".length
+    StringCharacterCount,
     ColorRgbaStruct,
     ColorHsvaStruct,
     ColorBrighter,
@@ -164,6 +168,8 @@ declare_builtin_function_types!(
     ItemFontMetrics: (Type::ElementReference) -> crate::typeregister::font_metrics_type(),
     StringToFloat: (Type::String) -> Type::Float32,
     StringIsFloat: (Type::String) -> Type::Bool,
+    StringIsEmpty: (Type::String) -> Type::Bool,
+    StringCharacterCount: (Type::String) -> Type::Int32,
     ImplicitLayoutInfo(..): (Type::ElementReference) -> crate::typeregister::layout_info_type(),
     ColorRgbaStruct: (Type::Color) -> Type::Struct(Rc::new(Struct {
         fields: IntoIterator::into_iter([
@@ -273,7 +279,10 @@ impl BuiltinFunction {
             BuiltinFunction::SetSelectionOffsets => false,
             BuiltinFunction::ItemMemberFunction(..) => false,
             BuiltinFunction::ItemFontMetrics => false, // depends also on Window's font properties
-            BuiltinFunction::StringToFloat | BuiltinFunction::StringIsFloat => true,
+            BuiltinFunction::StringToFloat
+            | BuiltinFunction::StringIsFloat
+            | BuiltinFunction::StringIsEmpty
+            | BuiltinFunction::StringCharacterCount => true,
             BuiltinFunction::ColorRgbaStruct
             | BuiltinFunction::ColorHsvaStruct
             | BuiltinFunction::ColorBrighter
@@ -342,7 +351,10 @@ impl BuiltinFunction {
             BuiltinFunction::SetSelectionOffsets => false,
             BuiltinFunction::ItemMemberFunction(..) => false,
             BuiltinFunction::ItemFontMetrics => true,
-            BuiltinFunction::StringToFloat | BuiltinFunction::StringIsFloat => true,
+            BuiltinFunction::StringToFloat
+            | BuiltinFunction::StringIsFloat
+            | BuiltinFunction::StringIsEmpty
+            | BuiltinFunction::StringCharacterCount => true,
             BuiltinFunction::ColorRgbaStruct
             | BuiltinFunction::ColorHsvaStruct
             | BuiltinFunction::ColorBrighter

diff --git a/internal/compiler/generator/cpp.rs b/internal/compiler/generator/cpp.rs
@@ -3553,6 +3553,12 @@ fn compile_builtin_function_call(
             ctx.generator_state.conditional_includes.cstdlib.set(true);
             format!("[](const auto &a){{ float res = 0; slint::cbindgen_private::slint_string_to_float(&a, &res); return res; }}({})", a.next().unwrap())
         }
+        BuiltinFunction::StringIsEmpty => {
+            format!("{}.empty()", a.next().unwrap())
+        }
+        BuiltinFunction::StringCharacterCount => {
+            format!("[](const auto &a){{ return slint::cbindgen_private::slint_string_character_count(&a); }}({})", a.next().unwrap())
+        }
         BuiltinFunction::ColorRgbaStruct => {
             format!("{}.to_argb_uint()", a.next().unwrap())
         }

diff --git a/internal/compiler/generator/rust.rs b/internal/compiler/generator/rust.rs
@@ -2929,6 +2929,10 @@ fn compile_builtin_function_call(
             quote!(#(#a)*.as_str().parse::<f64>().unwrap_or_default())
         }
         BuiltinFunction::StringIsFloat => quote!(#(#a)*.as_str().parse::<f64>().is_ok()),
+        BuiltinFunction::StringIsEmpty => quote!(#(#a)*.is_empty()),
+        BuiltinFunction::StringCharacterCount => {
+            quote!( slint::private_unstable_api::re_exports::UnicodeSegmentation::graphemes(#(#a)*.as_str(), true).count() as i32 )
+        }
         BuiltinFunction::ColorRgbaStruct => quote!( #(#a)*.to_argb_u8()),
         BuiltinFunction::ColorHsvaStruct => quote!( #(#a)*.to_hsva()),
         BuiltinFunction::ColorBrighter => {

diff --git a/internal/compiler/llr/optim_passes/inline_expressions.rs b/internal/compiler/llr/optim_passes/inline_expressions.rs
@@ -111,6 +111,8 @@ fn builtin_function_cost(function: &BuiltinFunction) -> isize {
         BuiltinFunction::ItemFontMetrics => PROPERTY_ACCESS_COST,
         BuiltinFunction::StringToFloat => 50,
         BuiltinFunction::StringIsFloat => 50,
+        BuiltinFunction::StringIsEmpty => 50,
+        BuiltinFunction::StringCharacterCount => 50,
         BuiltinFunction::ColorRgbaStruct => 50,
         BuiltinFunction::ColorHsvaStruct => 50,
         BuiltinFunction::ColorBrighter => 50,

diff --git a/internal/compiler/lookup.rs b/internal/compiler/lookup.rs
@@ -977,9 +977,22 @@ impl<'a> LookupObject for StringExpression<'a> {
                 )),
             })
         };
+        let function_call = |f: BuiltinFunction| {
+            LookupResult::from(Expression::FunctionCall {
+                function: Box::new(Expression::BuiltinFunctionReference(
+                    f,
+                    ctx.current_token.as_ref().map(|t| t.to_source_location()),
+                )),
+                source_location: ctx.current_token.as_ref().map(|t| t.to_source_location()),
+                arguments: vec![self.0.clone()],
+            })
+        };
+
         let mut f = |s, res| f(&SmolStr::new_static(s), res);
         None.or_else(|| f("is-float", member_function(BuiltinFunction::StringIsFloat)))
             .or_else(|| f("to-float", member_function(BuiltinFunction::StringToFloat)))
+            .or_else(|| f("is-empty", function_call(BuiltinFunction::StringIsEmpty)))
+            .or_else(|| f("character-count", function_call(BuiltinFunction::StringCharacterCount)))
     }
 }
 struct ColorExpression<'a>(&'a Expression);

diff --git a/internal/interpreter/Cargo.toml b/internal/interpreter/Cargo.toml
@@ -135,6 +135,7 @@ spin_on = { workspace = true, optional = true }
 raw-window-handle-06 = { workspace = true, optional = true }
 itertools = { workspace = true }
 smol_str = { workspace = true }
+unicode-segmentation = "1.12.0"
 
 [target.'cfg(target_arch = "wasm32")'.dependencies]
 i-slint-backend-winit = { workspace = true }

diff --git a/internal/interpreter/eval.rs b/internal/interpreter/eval.rs
@@ -909,6 +909,26 @@ fn call_builtin_function(
                 panic!("Argument not a string");
             }
         }
+        BuiltinFunction::StringIsEmpty => {
+            if arguments.len() != 1 {
+                panic!("internal error: incorrect argument count to StringIsEmpty")
+            }
+            if let Value::String(s) = eval_expression(&arguments[0], local_context) {
+                Value::Bool(s.is_empty())
+            } else {
+                panic!("Argument not a string");
+            }
+        }
+        BuiltinFunction::StringCharacterCount => {
+            if arguments.len() != 1 {
+                panic!("internal error: incorrect argument count to StringCharacterCount")
+            }
+            if let Value::String(s) = eval_expression(&arguments[0], local_context) {
+                Value::Number(unicode_segmentation::UnicodeSegmentation::graphemes(s.as_str(), true).count() as f64)
+            } else {
+                panic!("Argument not a string");
+            }
+        }
         BuiltinFunction::ColorRgbaStruct => {
             if arguments.len() != 1 {
                 panic!("internal error: incorrect argument count to ColorRGBAComponents")

diff --git a/tests/cases/types/string_character_count.slint b/tests/cases/types/string_character_count.slint
@@ -0,0 +1,96 @@
+// Copyright © SixtyFPS GmbH <[email protected]>
+// SPDX-License-Identifier: GPL-3.0-only OR LicenseRef-Slint-Royalty-free-2.0 OR LicenseRef-Slint-Software-3.0
+
+export component TestCase  {
+    property<string> empty;
+    property<string> hello: "hello";
+    property<string> hiragana: "あいうえお";
+    property<string> surrogate-pair: "😊𩸽";
+    property<string> variation-selectors: "👍🏿";
+    property<string> combining-character: "パ";
+    property<string> zero-width-joiner: "👨‍👩‍👧‍👦";
+    property<string> region-indicator-character: "🇦🇿🇿🇦";
+    property<string> emoji-tag-sequences: "🏴󠁧󠁢󠁥󠁮󠁧󠁿";
+
+    // is-empty
+    out property<bool> is-empty: empty.is-empty;
+    out property<bool> is-not_empty: !hello.is-empty;
+    out property<bool> test-is_empty: is_empty && is_not_empty;
+
+    // character-count
+    out property<int> empty-character-count: empty.character-count;
+    out property<int> hello-character-count: hello.character-count;
+    out property<int> hiragana-character-count: hiragana.character-count;
+    out property<int> surrogate-pair-character-count: surrogate-pair.character-count;
+    out property<int> variation-selectors-character-count: variation-selectors.character-count;
+    out property<int> combining-character-character-count: combining-character.character-count;
+    out property<int> zero-width-joiner-character-count: zero-width-joiner.character-count;
+    out property<int> region-indicator-character-character-count: region-indicator-character.character-count;
+    out property<int> emoji-tag-sequences-character-count: emoji-tag-sequences.character-count;
+    out property<bool> test_character-count: empty-character-count == 0
+        && hello-character-count == 5
+        && hiragana-character-count == 5
+        && surrogate-pair-character-count == 2
+        && variation-selectors-character-count == 1
+        && combining-character-character-count == 1
+        && zero-width-joiner-character-count == 1
+        && region-indicator-character-character-count == 2
+        && emoji-tag-sequences-character-count == 1;
+}
+
+
+/*
+
+```cpp
+auto handle = TestCase::create();
+const TestCase &instance = *handle;
+assert(instance.get_is_empty());
+assert(instance.get_is_not_empty());
+assert(instance.get_test_is_empty());
+assert(instance.get_empty_character_count() == 0);
+assert(instance.get_hello_character_count() == 5);
+assert(instance.get_hiragana_character_count() == 5);
+assert(instance.get_surrogate_pair_character_count() == 2);
+assert(instance.get_variation_selectors_character_count() == 1);
+assert(instance.get_combining_character_character_count() == 1);
+assert(instance.get_zero_width_joiner_character_count() == 1);
+assert(instance.get_region_indicator_character_character_count() == 2);
+assert(instance.get_emoji_tag_sequences_character_count() == 1);
+assert(instance.get_test_character_count());
+```
+
+```rust
+let instance = TestCase::new().unwrap();
+assert!(instance.get_is_empty());
+assert!(instance.get_is_not_empty());
+assert!(instance.get_test_is_empty());
+assert_eq!(instance.get_empty_character_count(), 0);
+assert_eq!(instance.get_hello_character_count(), 5);
+assert_eq!(instance.get_hiragana_character_count(), 5);
+assert_eq!(instance.get_surrogate_pair_character_count(), 2);
+assert_eq!(instance.get_variation_selectors_character_count(), 1);
+assert_eq!(instance.get_combining_character_character_count(), 1);
+assert_eq!(instance.get_zero_width_joiner_character_count(), 1);
+assert_eq!(instance.get_region_indicator_character_character_count(), 2);
+assert_eq!(instance.get_emoji_tag_sequences_character_count(), 1);
+assert!(instance.get_test_character_count());
+```
+
+```js
+var instance = new slint.TestCase({});
+assert(instance.is_empty);
+assert(instance.is_not_empty);
+assert(instance.test_is_empty);
+assert.equal(instance.empty_character_count, 0);
+assert.equal(instance.hello_character_count, 5);
+assert.equal(instance.hiragana_character_count, 5);
+assert.equal(instance.surrogate_pair_character_count, 2);
+assert.equal(instance.variation_selectors_character_count, 1);
+assert.equal(instance.combining_character_character_count, 1);
+assert.equal(instance.zero_width_joiner_character_count, 1);
+assert.equal(instance.region_indicator_character_character_count, 2);
+assert.equal(instance.emoji_tag_sequences_character_count, 1);
+assert(instance.test_character_count);
+```
+
+*/