Proposal: Embedded Expressions for String Statements (original) (raw)

Jeremy Manson jeremy.manson at gmail.com
Sun Mar 15 14:06:17 PDT 2009

Fair enough. I guess I'm too used to that; I just put parentheses everywhere.

On the flip side, I'm not a big fan of { as a delimiter. It seems to me that there should be a way to unify the general desire for better String handling (escaped Strings, multi-line Strings, embedded expressions). Can we colonize the ` (back-tick) character and start Strings over again from scratch?

Jeremy

On Sun, Mar 15, 2009 at 1:23 PM, Neal Gafter <neal at gafter.com> wrote:

By properly nesting the embedded expressions, it helps address precedence puzzlers such as this

System.out.println("2 + 2 is " +  2+2); Which declares that 2+2 is 22. On Sun, Mar 15, 2009 at 12:57 PM, Jeremy Manson <jeremy.manson at gmail.com> wrote: Hi Stefan,

I'm sure this is obvious to everyone who isn't me, but I'm not sure what the big win is here.  Basically, it looks to me as if you save a very small number of keystrokes:  String name = "Dave"; Old:  System.out.println("Hello, " + name + "!"); New:  System.out.println("Hello, {name}!"); ADVANCED EXAMPLE:  Object product = produce(); Old:  log("We " + (product == null ? "failed" : "produced " + product) + "!"); New:  log("We {product == null ? "failed" : "produced {product}"}!"); Again, I'm sure there is a motivation here, but I'm not exactly sure what it is? Jeremy On Sun, Mar 15, 2009 at 12:15 PM, Stefan Schulz <schulz at e-spirit.de> wrote: Howard mentioned it before, embedding expressions might be a nice thing to have in Java. The simplest thing is to embed variables to print their value. The proposal is not at the same level as Multi-line Strings, as it does not result in a construction of a String Literal but rather offers a "short cut" for building complex Strings. To at least have a basis for discussion, I set up a proposal that IMO could fit in the scope of COIN.

Stefan

Proposal: Embedded Expressions for String Statements AUTHOR(S): Stefan Schulz VERSION: 1.0    Initial version. Formatted version: http://docs.google.com/Doc?id=ddhp95vd11dv7rmrcp OVERVIEW FEATURE SUMMARY: Often, textual output is constructed of a mix of plain text and values resolving from expressions. An escape sequence allows embedding such expressions into a string. If the result of the expression is no String, it will be converted to one. MAJOR ADVANTAGE: Improves readability and eases String construction. MAJOR BENEFIT: Reduces the cluttering in writing textual output. MAJOR DISADVANTAGE: May encourage to write one-liners with many expressions inside a String construction. ALTERNATIVES: Write strings the old way by using concatenations or using builders. EXAMPLES SIMPLE EXAMPLE: String name = "Dave"; System.out.println("Hello, {name}!"); ADVANCED EXAMPLE: Object product = produce(); log("We {product == null ? "failed" : "produced {product}"}!"); DETAILS SPECIFICATION: The new escape sequence { will be handled at compile time by transforming the string statement into a concatenation of Strings. Neither can the statement be understood as a String literal nor is it an escape sequence in the sense of representing a single character literal. Therefore, the transformation has to be done prior to any other escape sequence handling. Changes are required in the JLS §3.10.5 "String Literals" and 3.10.6 "Escape Sequences for Character and String Literals". Although the new escape sequence does not form a part of a String literal, it must be stated that it's a legit escape sequence with the consequence of making the string sequence become a statement rather than a literal. A new chapter is to be introduced on embedding expressions in string sequences, which closely relates to §15.18.1 "String Concatenation Operator +". The syntax would be as follows: EmbeddedExpressionStatement: " StringCharactersAndExpression StringCharactersOpt " StringCharactersAndExpression StringCharactersOpt EmbeddedExpression StringCharactersAndExpressionOpt EmbeddedExpression \ { Expression } Note: The sequence "{exp}" is deliberately chosen as it resembles the way other languages provide a similar ability, e.g., JavaFX ("{exp}"), PHP, Python and Groovy ("${exp}"). COMPILATION: In general, the statement will be transformed into a concatenation of literals and expressions. In the following, the String Concatenation Operator is being used, but maybe replaced by a StringBuilder solution. The latter might be easy to do, as the transformation happens before literal processing. Transformed simple example: String name = "Dave"; System.out.println("Hello, " + name + "!"); Transformed complex example: Object product = produceSomething(); log("We " + (product == null ? "failed" : "produced " + product) + "!"); TESTING: The transformation has to be tested to resolve to the expected old style way of concatenating Strings. The cases should cover simple variable references (null, primitive, String, and Object) as well as simple and nested expressions (including nested expressions with Strings having embedded expressions). LIBRARY SUPPORT: None. REFLECTIVE APIS: None. OTHER CHANGES: None. MIGRATION: Replace existing old style concatenation by applying the new escape sequence. COMPATIBILITY BREAKING CHANGES: None. The escape sequence { would prior have caused a compiler error. EXISTING PROGRAMS: No changes. REFERENCES EXISTING BUGS: (Although it is to be assumed there are existing bugs/rfes, the search did not pop up results for the keywords used. So this remains to be done.) URL FOR PROTOTYPE (optional): None of yet.

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