use string sections to reduce result accumulator size

src/placeholder.ts

@@ -77,10 +77,12 @@ class Substitutor {
   }
 
   replace(): string {
-    const result: string[] = [];
+    const result: (string | StringSection)[] = [];
 
     let escaping = false;
     let hasSuffix = false;
+    let sectionOffset = -1;
+    let sectionLength = 0;
 
     while (this.#pos < this.#input.length) {
       const c = this.#input.charAt(this.#pos);
@@ -90,7 +92,21 @@ class Substitutor {
         escaping = false;
       } else if (c === this.#substitutor.escapeChar) {
         escaping = true;
+
+        if (sectionOffset >= 0) {
+          result.push(this.#input.subSection(sectionOffset, sectionLength));
+
+          sectionOffset = -1;
+          sectionLength = 0;
+        }
       } else if (this.tryAdvance(this.#substitutor.pattern.prefix)) {
+        if (sectionOffset >= 0) {
+          result.push(this.#input.subSection(sectionOffset, sectionLength));
+
+          sectionOffset = -1;
+          sectionLength = 0;
+        }
+
         const innerSubstitutor = new Substitutor(this.#substitutor, this.#input.subSection(this.#pos), true);
         const variable = innerSubstitutor.replace();
 
@@ -111,22 +127,26 @@ class Substitutor {
         this.#pos += innerSubstitutor.#pos;
 
         continue;
-      } else if (this.tryAdvance(this.#substitutor.pattern.suffix)) {
-        if (this.#inner) {
-          hasSuffix = true;
-          break;
+      } else if (this.#inner && this.tryAdvance(this.#substitutor.pattern.suffix)) {
+        hasSuffix = true;
+        break;
+      } else {
+        if (sectionOffset < 0) {
+          sectionOffset = this.#pos;
         }
 
-        throw new PlaceholderException(this.#input.getSection(), this.#pos, "Missing prefix");
-      } else {
-        result.push(c);
+        sectionLength++;
       }
 
       this.#pos++;
     }
 
+    if (sectionOffset >= 0) {
+      result.push(this.#input.subSection(sectionOffset, sectionLength));
+    }
+
     if (this.#inner && !hasSuffix) {
-      throw new PlaceholderException(this.#input.getSection(), this.#pos, "Missing suffix");
+      throw new PlaceholderException(this.#input.getSection(), this.#pos, "Missing variable end delimiter");
     }
 
     return result.join("");

src/string-section.ts

@@ -44,4 +44,12 @@ export class StringSection {
   public substring(beginIndex: number = 0, endIndex: number = this.#length - beginIndex) {
     return this.#parent.substring(this.#offset + beginIndex, this.#offset + endIndex);
   }
+
+  public toJSON() {
+    return this.getSection();
+  }
+
+  public toString() {
+    return this.getSection();
+  }
 }